how should i charge this battery?

Hi, You have NiCads. Nominal 1.2 volts per cell. A rule of thumb (nice and safe) is to charge at 1/10 the mAH rating for 10 Hrs. At that rate the NiCad temperature usually does not need to be monitored. In practice you really won't get 1000 mAH out of the parallel pack but you will get more than 400 mAH. The voltage could be about 1.4 volts per cell. When charging in series it is really desired that the battery packs be all the same type and rating. Series by definition passes the same current through all cells. If you ask me I would charge the packs separately. I would use 4.2 volts per pack and limit the maximum current to about 40 mA. Do you have a way to control the current? A discharged battery will draw more current than a partially charged battery but keep the maximum to about 40 mA and charge over night. This is not the optimum charging for the batteries but will do the job. Regards, Tom

Wiring them in parallel isn't a very good solution, unless you use diodes to prevent one from running current through the other. Unfortunately, that will waste a bit of the output voltage.

A better solution would be a larger pack, since it would probably be lighter too. You can get 1700mAH 1.2V nimh batteries for a buck each, and wire 4 together.

look for

HR-AAU overstock w/TABS

It'll be lighter, and you won't have to worry about cross-charging.

Your homemade 1000mAH pack needs about 100mA for 14 hours. Take care not to overcharge it, or you'll kill the nicads. You can tell when you are overcharging it, because the cells heat up quickly.

--
Regards,
  Bob Monsen

If a little knowledge is dangerous, where is the man who has
so much as to be out of danger?
                                  Thomas Henry Huxley, 1877

You need to charge them separately. It's simple & cheap. Get a 12V DC wallwart, 2 LM317 voltage regulators and 2 resistors. Wire it up like this:

---------

+12V ----+-----in| LM317 |out------+---Batt1--+ | --------- | | | | | | | +---/\\/\\/\\-----+ | | R1 | | | | | | --------- | +-----in| LM317 |out------+---Batt2--+ --------- | | | | | +---/\\/\\/\\-----+ | R2 | Neg----------------------------------------------+

Batt1 is the 400 mAh pack, batt2 is the 600 mAh pack. R1 is a 33 ohm resistor. R2 is a 24 ohm resistor.

Be *sure* to connect batt1 to the 33 ohm resistor and batt2 to the 24 ohm resistor. Note that the batteries are *not* in parallel or series. The negative side of both batteries goes to the negative from the wallwart. The positive side of each battery goes to its own LM317/resistor combination. Charge for 14 hours.

Do not use these batteries in series. Doing so could damage the 400 mAh pack.

Ed