I know many people are looking to do lithium conversions on Gems but maybe confused about how it all works . Lets try and explain a few things .
There are many different types of lithium battery chemistries . They all have different pluses and minuses and are used for different applications . The lithium battery in your phone and laptop is completely different from the kind you would use in a boat or a car , you would Never use this type of battery in a Gem or EV . The Lifepo4 chemistry you would use in a boat or car starting battery is completely different from what car manufactures use in EV’s . Most all Ev’s use one type ( except Tesla , theirs is different) . So When someone says lithium it doesn’t tell you anything . For the purpose of this I will focus on the 2 chemistries that would apply to use in a Gem .
First is LiFepo4(also known as LFP) . These are the square cells you see . (the green cells Inwo sold are these chemistries ) If you buy a drop in replacement for your car or boat they will be Lifepo4 chemistry . These are one of the safest chemistries available , They are thermally stable to 518 degrees . There are hundreds of Youtube videos of manufacturers putting nails thru them, shooting them , charging them to twice their max voltage . In almost all cases they smoke but don’t catch on fire .But heat them to 518 degrees and they will .
Many people consider them safer than a flooded lead battery . Try to charge a lead 12v battery to 24v and it will go boom . These are a consumer lithium battery and widely sold . No car maker uses these in an EV . The reason is low power density and voltage . They do not hold as much power for their size or weight as other lithium . And They have a lower voltage per cell so you need more of them for an application . These work great in a gem but you need 25 to 28 for a Gem . They require a lot of connections to make a pack so more possibilities of connection problems .
NMC (also known as NCM) This is the Chemistry Chevy , Nissan , Jaquar , BMW , Mercedes and every other manufacturer uses . Most of the batteries used in Gems come from one of the EV cars . They have evolved nicely over the last few years . The trick here is to get modules that can be configured to work well in Gems . You want 20 -24 cells in a Gem . So modules that come in 14 or 16 cells don’t work . You want a minimum of about 65h . This would match a set of gels for range . Smaller cells set up in a parallel/serial application can work but make for a difficult install and monitoring . If you are buying used cells you want to get ones that have been tested . All batteries lose capacity over time and lots will not be anywhere close to their once rated capacity . Nissan leaf cells are rated at 64ah new . Nissan considers them end of life at 80% capacity , under that they are removed from service . These are the thousands you see sold on Ebay . Most test about 70%, this means they are now 44ah . This can apply to any battery and explains why some people don’t get the results they are looking for . NMC is also considered a safe chemistry and is Thermally stable to 410 degrees .
Other things to know . Don’t charge any of them to 100% . All lithium lasts much longer if only charged to the low 90% range . If discharged lower than minimum voltage most will be permanently damaged . They may take a charge but will probably swell and will have diminished capacity . Always use a BMS . A good BMS will keep your cells balanced , won’t allow over charging and will disconnect your battery if voltage gets too low to protect it. A properly designed lithium conversion should give you years of service and be safe to operate .Any questions let me know .