# Simple Battery Question

I have a nice rechargeable battery. It was a lipo I think. (I took picture of it below) My charger broke, I would like to know how to charge the battery. the charger output was 9.6 volts 300 ma What will happen if I give it 9 volts or 10 volts or even 11? also what happens if I give it more amps than 300 ma?

Says on it that it is NiMH. Nickel Metal Hydride. Probably 8 AA size cells, 1.2V, wired in series.

This will charge them slowly. http://www.all-battery.com/15V400mAhUniversalSimpleChargerFor8.4V-12VBatteryPack-01008.aspx

Note that the rate of charge is a function of the voltage you're charging with; the charge current is directly related to the difference between the battery and your source.

This explains using an LM317 and also limiting the output current: www.national.com/ms/LB/LB-35.pdf

Charging lithium and NiMH batteries is more involved than supplying voltage. You have to monitor the correct ending conditions, some of which (-dV/dT ...) are nasty.

Chagrin's comment is wrong -- when full, a NiMH battery will have a negative voltage change for an increase in current. That's how you tell they are full -- when the temperature rises more than 3*C or so in some short time period (2 or 3 minutes), and the terminal voltage falls.

The usual charging profile is 1.55 volts per cell, then terminate the charge when the temperature rises faster than the cutoff, or the voltage drops more than a few millivolts per cell. To play it safe, pick a smaller value, say, 1.50 volts per cell, and reduce the charging current (use a PWM pin to control a transistor that's supplying current to the batteries) whenever the voltage rises. The OP can measure the voltage with a voltage divider -- be sure to use precision resistors.

Nimh battery chargers are quite cheap here in the UK and may be cheap where you are too - in that case I suggest you get one, if you plan to fast charge this battery.

Alternatively, if the idea of spending a couple of bucks isn't an option you can trickle charge it. Batteries tend to be less fussy about being overcharged when they are trickle charged. For NiCd batteries, the trickle charging formula was 16 hours charging at the '12 hour' rate i.e. from the battery's nominal capacity work out how much current it would need to fully charge it over 12 hours, and then charge it at that current for 16 hours.

For anything involving lithium, I'd say it is potentially dangerous to use anything other than a properly designed battery charge suitable for that type/size of battery, but I think NiCd and Nimh are not as critical.

what happens if I just plug 10 volts or 9 volts directly into it via AC-DC adapter

Whatâ€™s wrong with spending \$7 and not run the risk of blowing up the battery?

http://www.all-battery.com/15V400mAhUniversalSimpleChargerFor8.4V-12VBatteryPack-01008.aspx

arduinopi: what happens if I just plug 10 volts or 9 volts directly into it via AC-DC adapter

How important is it to you that you don't wreck your battery or the thing you're trying to charge it with?

If you have a battery and chargers that you don't care about then nothing wrong with just plugging things together to see what happens. But if you want the battery charged without damaging it and want to avoid overcharging the battery or overloading the charger, do it properly with the right charger. The battery probably costs more than the charger; just how desperate are you to avoid spending a couple of bucks?