Battery Series and Parallel Question

[Fixinit]

Hi. Thanks for all of the valuable information on these forums.

I am Building an ebike and want to use the Milwaukee 18v high output 12.0ah battery on my bike. You can currently get one 12.0ah and one 6.0ah with a charger for $250. Here is my question. If I use 2 of the 18v 12.0ah in series that would give me 36v at 12ah. If I wire 2 of the 18v 6.0ah in parallel that would give me 12ah increase to the the batteries in series. Would there be any problem doing this? At some point as the budget allows I would like to add another battery to the series making it 54v at 12ah. I probably would add the additional 6.0ah battery to the parallel circuit making it 18ah. I just am unsure of the different amp hours in the series and parallel circuits and if they could cause a problem. I know I should just build a battery pack but I like the modular approach of tool batteries plus these new packs use the 21700 cells and they have a 3 year warranty.

Thanks in advance for your reply.

 

[john61ct]

An increasing number of battery packs have internal circuitry, not just BMS but recording the charge / discharge history.

So don't expect warranty coverage for other uses.

IMO if you like those cells and buying them that way is good value strip them out and build your own packs.


> If I wire 2 of the 18v 6.0ah in parallel that would give me 12ah increase to the the batteries in series.

No, voltage of the smaller pack is still only 18V not at 36V.

 

[Fixinit]

So my best bet would be to use 3 of the 18v 12.0ah in series for 54 volts. I see what you are saying and not sure why I thought the 6.0ah would work in parallel

 

[john61ct]

I am saying you're rolling the dice as to whether it will work at all.

If worst case salvaging the cells is an option for you go for it

 

[999zip999]

Series with same ah pure pack they should be equal 4 best things. And that can be hard for some people to keep balance and to get full life out of the packs that you have paid for. Yes Milwaukee uses good cells. How about a big 54 volt 8ah or more ah per pack for those blowers and things. What are you running ?

 

[flat tire]

Tool packs blow. There is no need for modularity and they have extra stuff just wasting space and adding unecessary mass. Get a regular ebike battery that is made with the same cells as those tool packs but in a smaller space and single enclosure, plug it in, and RIDE!!

3 year warranty is unnecessary for new brand name canned cells since they are all incredibly reliable and long lived even if you are a little bit stupid as an owner.

 

[999zip999]

Ridgid tool batteries from Home Depot have a lifetime warranty that's to you die

 

[john61ct]

Not if used with other chargers or for purposes other than in their tools