# Can a charger made for 1600mah batteries safely and effectively charge 2500mah batteries?

I have several dead battery packs for my 18v power tools.  Planning to rebuild them and figuring I might as well upgrade their run time while I'm at it.  The original battery packs are 1600mah but I can get 2500mah battery cells that are the same size for about the same price.

1) Will I still be able to charge the higher capacity batteries with the charger that came with the lower capacity ones?

2) Will it charge them to their full 2500mah capacity?

3) Will it be able to detect when they are fully charged?

4) Will it give a false positive and think they are fully charged as soon as they reach the 1600mah of the original battery packs?

5 years ago
a. So long as the voltage is identical you should be okay.
b. Many battery packs have a chip/protection circuit in them to protect against over/uinder voltage/ short circuit. These may not play nice with new cells.
c. In a VERY loose sense, think of batteries as buckets, with Amp-hours as capacity. The charger is completely unaware of the capacity of a battery, as a hose is unaware of the capacity of the bucket with a float valve. It just keeps filling until it fills to the top, then stops. If there is no protection circuitry (think the float valve) and you apply too much voltage, it overflows, causing problems.

Voltage is the measure of charge level in a battery -- like a pressure (again, very much metaphor, not literal pressure) if you apply 1 volt to a battery it will charge up to 1 volt. it will keep accepting current until the 'pressure' equalizes between the circuit and the battery, at one volt. What does this imply? larger battery will charge to the same 1 volt as a smaller one, but it will take longer.

1) yes, most likely.
2) likely
3) yes
4) unlikely

**none of the above are absolutes, and do not preclude the possibility of said charging/protection circuits mucking things up.
etcmn (author) 5 years ago
Thanks for your answers. This was how I guessed it would work but as I'm not well versed in electronics I wanted to get some better informed opinions.

nurdee15 years ago
As long as the voltage is the same you are good to go. It will take longer to charge your large battery if you use the same charger as you did for the smaller one but it will power your tool for longer.