We have been doing a lot of testing since LiPo battery packs have been released for RC cars.
Comparing different packs, different C rated packs and other attributes, We have rejected a number of cells from different manufactures due to inconsistent balanced cells within the packs and and also by internal resistance.
The C rating is all well and good but how do you know if a high rated (e.g. 30C) rated pack is actually what is says on the packet.
We have tested LiPo of various C rating from different manufacturers and the differences really are amazing. Both on the track and by measuring internal resistance.
Normal NiCd and NiMh cells are very different to LiPo packs but one thing that remains a very good measure of a good battery is the internal resistance.
The lower the resistance the better the pack in terms of performance. The lower the resistance is the best indication of the C rating also.
The lower the rating, the higher the C rating.
The Demon DL4000 packs for example are rated at 30C(120 amp continuous) have an internal resistance of 3mOhm typical.
The Demon DL5000 which are rated at 20C (100 amp continuous) have 3 to 4mOhm
The Demon DL3600 which are rated at 25 C (90 amps continuous) have 4 mOhm.
We recently tested some 3800 packs from another manufacturer rated at 25C+ and they only gave 9mOhm internal. i.e. more than double the resistance.
Other manufacturers packs have shown figures of 12 mOhms or more.
Replacing these with a new low internal resistance LiPo pack of cells will transform a car in terms of speed and punch.
Note also that the power and capacity and long life of a LiPo is directly proportional to the weight, so there is no way a lightweight LiPo will deliver very high power for the full duration without fading and losing performance after fewer charges.
A high quality heavy LiPo will remain consistent and we have charged a DL5000 300 times without any loss of power.
Note that good quality LiPo cells also do not lose duration at different rates like NiMh cells. Therefore a quality LiPo will retain balance within the cells in the pack even after 100s of charges.
The balance connector is a means of testing a LiPo occasionally to give peace of mind and just to make sure all is ok. It is not necessary to charge with the balance lead every time, and we have charged Lipo packs 100s of times without the balance lead without any problem. Also that the pack will charge faster without the balance lead as the charger does not have to keep checking each cell.
No Cells or Animals where blown up in this testing. Thanks for listening.
Thanks
Nick