LiFePO4 replacement for (large) SLA

There are many LIFPO 12V batteries with built-in charge displays from 4 or 5 bars to LCD screens, and many also have Bluetooth or wi-fi and apps to see anything you want about the internal state. I'd start by browsing on Amazon, then go to YouTube and search for "Will Prowse", pick a video at random and click more to see all of the description and click the link to his website to see what brands he does and does not recommend.

That could be an advantage in your usage. Would you use same physical size of lithium or something intermediate to get a lighter machine?

The latest LiFePO4 are a lot less volatile than the earlier generation LiNiCo (etc) but I'm not sure I would want to sit on one if I was not able to run away from it PDQ. You have about 15s from the first signs of the magic smoke coming out to it venting to get away from it. Sparks and flames are more or less guaranteed with the old chemistry but the newer iron ones just get hot and emit copious white flammable solvent fog.

Not nice in an enclosed space and potentially problematic if there are any ignition sources nearby. Flashover fuel air explosion from the battery solvent mist is a real risk to firefighters in a confined space.

Main risks are over charging, over discharge(wrecks them) and physical damage. SLA by comparison are practically benign if rather heavy.

Provided you charge (and discharge) them properly they should be fine but there have been a lot of modded e-bikes going up in flames spectacularly after unwise (illegal) go faster modifications.

So long as you look after the battery it should be fine.

"While it is often marketed as a physical "drop-in" replacement, swapping chemistries transforms the electrical system from a passive chemical device into an active electronic component. This invalidates existing device safety certifications and triggers distinct logistics and environmental liabilities.

If the device or appliance was previously certified by an agency like Underwriters Laboratories (UL), swapping the battery chemistry voids the original equipment certification."

That's all you need to know. It means don't do it.

Batteries are almost universally inaccessible in use. They are usually hidden under the seat -- which may be designed to support a person weighing hundreds of pounds (up to 450!) *plus* the weight of the seat itself. My chairs each (originally) weighed about 300 pounds.

This is a video of the battery removal process for a similar chair:

Other "scooters" often have smaller battery packs -- some that even have handles to enable you to remove them easily from the scooter for charging or swap-out (keep a fully charged spare to replace a depleted one).

An "app" would likely not tell you much about the sort of usage you can get from the chair as it wouldn't know the rate at which you are likely to consume power (climbing hills, operating the various actuators on the chair, headlights, etc.).

But, could represent a "hook" to enable a BETTER app to be created to track this information despite the erroneous indications presented on the gas gauge.

He seems more focused on solar power applications? There, you don't have the same sort of constraints as in a wheelchair (size, shape, connections, etc.)

There are many sites that tout "lithium upgrades" for wheelchair battery packs. But, often are incomplete -- trying to sell the idea or a specific battery pack. They gloss over these issues (e.g., what charger will I be using? Will the wire that carries the charge current from the charger connection *to* the battery be sufficient to handle that current -- as it and the connectors along the way -- was likely sized for the charger sold with the SLA battery pack.

My lawyer points out that such a modification likely raises safety and liability issues (but, that's what lawyers are paid to think about!). OTOH, I'm not planning on SELLING such modifications but, rather, exploiting ONE modification to simplify *my* usage. (to reduce the maintenance issues that I face due to my LACK of use)

OToOH, if it proves to be that this modification enhances my application, then it leaves me in the position of having to figure out how to make it available while limiting my legal exposure.

When I was doing the certification to operate a fork lift, I asked the instructor how to handle an engine fire (you are seated ON an internal combustion engine with the fuel tank immediately behind your backrest).

"Get off the lift (keep in mind, the number one rule is that you have SECURED yourself to the vehicle lest you accidentally become separated from it!) and TRY to turn off the gas valve. Call the fire department and be sure to tell them you have a PROPANE FORK LIFT fire. They will arrive and PARK A BLOCK AWAY..."

I.e., YOU should put a similar distance between yourself and the fire and not just sit around watching it as a propane explosion will likely take out a whole block! Just how fast can you run? And, how disciplined are you NOT to watch a fire???

Hmmmm.... I had thought the whole point of the new one was safety. But, I guess that's a relative term...

The SLAs always are at risk of outgassing. Rarely a risk of spilled electrolyte -- though chairs can and do tip (usually because of carelessness on the driver's part -- trying to tackle too steep of a grade or failing to take approach it "head on").

The batteries are typically in a steel framework under the chair (see video linked elsewhere this thread). Ideally, sized to exactly fit that enclosure so there is no room for them to slide, tip over, etc. Of course, if the ENCLOSURE is tipped over, all bets are off; there is an assumption that the weight of the batteries holds them in place -- with the expectation that gravity operates on them in a specific orientation!

I thought the BMS handled all of those cases.

That has been the problem with the SLAs. As I don't "need" a chair, I keep mine stored in the garage. I periodically take it out for a drive around the neighborhood (~2 miles) to "exercise" the battery before reconnecting to the charger.

If I give a demo and need it to be fully charged, then I can reconnect it the night before and "top off" the battery. (Demos tend not to use much stored energy so even a partially discharged battery is often adequate)

But, in summer, it's just too damn hot to be driving around any time other than just before sunrise (while the chair has driving/backup/signal lights that make it reasonably safe to operate in the dark, doing so in the evening means contending with ~100F temperatures almost until midnight).

Add to that, the inhospitable environment in the garage and I usually end up having to address a battery issue. (I can often rescue a set of replacements that haven't sulfated -- but, that's still a chore to do the replacement)

From discussions, today, the concensus is:

- maintain the existing battery (regardless of the inconvenience) OR

- replace it each summer (though with a smaller pack that has just enough capacity for your "demo" needs)

I think I will opt for the second option -- using a smaller group size and "fleshing it out" to fill the same volume as the intended battery. This will save a few bucks *and* make it considerably easier to replace the batteries.

The main problem that would need more research, is that Lithium need a completely different regime in therms of charging, and also limiting discharge to level that does not destroy the battery. I would not consider it safe to just swap one for the other. Fire hazard, explosions, and threat to the safety of life. Not helpful if immobile in a wheelchair.

Stick to lead acid, but perhaps replace with deep discharge types.

This covers the conversion requirements:

That smells a lot like AI slop (including AI generated images). Not saying it's wrong, but I would not trust a company who markets their products as superior based on AI output. As AI does, it takes a lot of words to make its point.

When you're buying an LFP pack, it comes with a BMS which is intended to protect the battery from over voltage, over discharge, over temperature - it isolates the battery if it detects any of those. The quality of BMSes... varies. As does the physical construction of the pack - eg fusing, cell pressure and mechanical protection.

But the main issue is you need to replace the charger, and if it's in a system that expects lead acid charging behaviour (eg cars with alternators) then that's a problem.

Also things that rely on the internal resistance of lead acid may not be happy with a different chemistry. And cold temperatures are a problem too (unless you go sodium ion, which has different challenges).

OTOH if the system is uncomplicated - (replaceable) external charger charges battery to full offline; vehicle discharges to empty; repeat - then there's more chance of success.

Another option is to get some prismatic LFP cells from CATL or EVE (via intermediaries - they don't sell direct) and do your own mounting and add a commercial BMS. By DIYing you can aim for quality. Although testing is then your problem (and you do need to avoid shady sellers giving you relabelled reject cells).

Theo

charging -- because the "charging port" on most chairs is located at the tip of an armrest, as part of the "joystick controller" assembly. A single conductor that brings B+ to the controller acts to deliver charge current to the battery.

This conductor passes through several connectors that have been sized for the charging current delivered by the "best" SLA charger. Sizing a charger for a lithium pack typically delivers considerably higher charge currents which likely aren't expected in the original design. So, I'd have to deliberately downsize the charger (which means any attempt to exploit the additional capability of the lithium would be met with INCREASED charge times beyond the typical "overnight")

I'd have to reprogram some of the operating parameters of the motor controller but that's relatively easy (if you have the correct tools and understand what all of the parameters mean and their effect on the chair's use).

I still think the most effective (for MY use case) approach is to install smaller (much easier to man-handle than 50-pounders!) SLAs and fabricate an "outer shell" to ensure they religiously comply with the size and shape of the original battery group as the "packaging" relies on a tight fit to keep things in place.

Newer chairs designed to exploit the battery chemistry are designed with that in mind, not as an afterthought. The folks I know who have done such conversions have taken that more "wholistic" approach to the problem. But, their motivations are far more practical than mine; I just need the chair to be "available" for my short little dog-and-ponies without having to panic because the existing batteries have gone flat forcing me to get them replaced on short notice.

The charger is the main *electrical* issue. But, it's not a simplistic "charger->two wires->battery" model (as it MAY be in some applications).

We looked at the wiring diagram and schematic for the electronics in

E.g., the size of the conductor from the charging port to the physical battery, the number (and type) of connectors it passes through, the effect on the "system" if the battery is disconnected (e.g., main circuit breaker opened), the attachment to the battery, the effect of charge cycles on the battery in a tight, unventilated space, etc.

The other (perhaps MORE) important issues are physical; e.g., the battery is inaccessible during use and charging, the battery is not physically secured in place (relying on size and mass to keep it where intended), the locations of the "binding posts" for the batteries, their weight (a battery with insufficient mass is going to be tossed around in normal use -- a wheelchair ride is NOT "smooth")

Cold, here, is a non issue. I don't think we saw a single "below freezing" day in the past two years (and that assumes storing the chair outdoors).

Heat, OTOH, is a pisser and eats SLAs in short order (one replaces the starting battery for their vehicle religiously at 36 month intervals to avoid being "disappointed" by it!)

You can't discharge to a point below which the controller locks out action (based on *its* notion of state of charge). This leaves the "driver" stranded (an electric wheelchair without power is like pushing a wagon without wheels -- the weight of the chair plus occupant is 500-600 pounds and the drive is far from frictionless, even when disengaged).

That requires a lot of work and assumption of liability. When you don't have control over -- or detailed knowledge of -- your load, thats a crap-shoot.

I.e., I would never consent to doing such a modification for someone, even if all of the "tough thinking" had been sorted out. Now, YOU are stuck as the support system for that "product".

By contrast, "buy THESE batteries, call me when they are on hand and I'll come over to replace the old ones" is a low risk, easy to gauge task, thankless as it may be.

For most users who NEED a chair, I think insurance/gummit covers routine replacement (~5 yrs) so there is less concern *if* you can eke that amount of service life out of your existing kit. But, this requires attention to maintenance, etc. (clearly not something that

For example, when the batteries *die* in the chair, you have to elevate the seating assembly to gain access to the battery compartment (even removing the cosmetic cover is difficult without this step).

The "approved" method of doing this is to remove the seat cushions and thread a long (12"?) tool through the (metal) seat bottom to engage a screw drive that allows you to manually "drive" the elevator mechanism.

Of course, there is some serious gear reduction involved to lessen the load on the elevator motor (you don't need fast response from the elevator as its range of motion is O(8 inches).

But, you can isolate the "dead" battery pack by opening the main circuit breaker.

And, back feed "battery voltage" to the charging port (often an XLR connector in the joystick controller) to make SOME power available to the elevator motor. AFTER taking care to disable the "inhibit" function that prevents any motion while the "charger" is connected.

BUT, all of the power to the chair mechanisms is now being fed through the circuit path that was originally intended to carry ONLY charger current. So, don't accidentally engage the drive motors, etc. even if your back fed power might be capable of operating the chair IF CONNECTED *AS* THE BATTERY.

No, that means "don't do it for someone else or commercially".

People routinely modify their chairs, altering safety-related issues /for themselves/. These can be retuning the controls to be more responsive -- despite the driver's ability to CONTROL the chair with those modifications. Or, oversized tires to better navigate outdoor terrain (yet complicate operation in an existing structure). Or, boosting the top speed (most chairs run at ~6MPH but I have seen chairs that can do 15MPH. Controlling such a chair on "typical driving surfaces" is almost impossible -- even with a joystick (with a mouthstick or any other physical shortcoming, next to impossible. Or, disabling the inhibit on operation while charging. Or, with seat elevated. Or...

And, you know SOMEONE likely made those modifications (for a price!) for those drivers!