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Any item you buy has implicit some liability insurance associated with it. Thus if it causes major damage, you can sue the manufacturer. Of course, this explains why all the wall warts comes from China. "Honest judge, the ACME manufacturing company doesn't touch the AC power line. Blame XXXX for that dangerous wall wart."
Hopefully you have a watchdog timer in your charger. You can't take the risk that the PIC goes off in a loop and whacks the battery. Also, current sense using the power fet seems way too inaccurate.
Generally most manufacturer provide an independent battery protection scheme as a safety, i.e. independent of electronics. In nicad packs, it could be a PEPI. Having designed charger chips, I know you need multiple protection schemes.
While you may have considered the possible states of a healthy gel cell, you also need to consider the state of a gel cell on it's last legs. You don't want to charge a battery that is not healthy.
I want to run accessories on the gel cells. It's a bummer to have your notebook computer or whatever drain your car battery when you are in a remote area. So with the car not running, the gel cells are the power source. With the car running, the alternator is the power source. That is mostly what battery isolators do, and they would be fine if the auxiliary battery could take the alternator voltage. [The isolator uses relays to prevent reverse power, i.e. the auxiliary battery does not get used to start the car.] Gel cells cant take as much voltage as "regular" car batteries since they don't vent.
To make it more complicated, I'd like to not use switchers. I want to be able to use ham radios and scanners from these gel cells, so I don't want the RF hash from a switcher. So basically I need to provide the float voltage to the gel cell from the alternator, i.e. high current low dropout regulator with a bit of tempco compensation for the gel cell. Reverse power needs to be prevented. Now this regulator will see the load of the electronics, which could be high if a HF transceiver were attached. Thus you wouldn't current limit this regulator, but put a bidirectional current limit on the gel cell. Probably something like a polyswitch would do the trick, though they have really wide specs.
What I do now is for long periods in the boonies, I bring 5 gel cells that I charge prior to the trip. For charging, I use an off the shelf
3 state charger since I don't care about switching noise in my garage. These are 50 to 70 AHr batteries picked up on the surplus market (data center pulls). When a battery reaches 10V, it gets retired and I use the next battery.