N o a h ?

Batteries

I have a chal­leng­ing rela­tion­ship with bat­ter­ies. I don’t like hav­ing to replace them; I don’t like hav­ing to charge them. Finally, I tried to under­stand them, at least some of them (Li⁺ chemistries).

In this section

• A frame­work for build­ing lithium-ion bat­ter­ies
• Dimen­sion­ing cell-to-cell con­nec­tions
• Build­ing and using the kWeld spot welder
• Assem­bling a 4s LFP bat­tery

Battery-building communities

My ini­tial inter­est is in RC appli­ca­tions because I had safety con­cerns about the com­mon use of unpro­tected LiPo bat­ter­ies. There are very few peo­ple in RC build­ing their own bat­ter­ies. I sup­pose the off-the-shelf LiPos work fine for vir­tu­ally every­one, but they’re just not to my taste. Rad­i­cal RC will build you a pack from very nice Lithium Werks cells, but they still have exposed bal­ance leads instead of an inte­grated BMS.

On the other hand, I’ve found these com­mu­ni­ties to have enthu­si­as­tic bat­tery builders, maybe too enthu­si­as­tic even:

• Elec­tric skate­board­ers, who have a stun­ningly high bar for safety and many good ideas about how to build packs. Their bat­ter­ies are put through a ton of abuse, for bet­ter or worse.
• Elec­tric bicy­clists, also with a lot of good ideas. More care­free than elec­tric skate­board­ers, but still smart enough to know their bat­ter­ies need to sur­vive a lot of jostling.
• Sta­tion­ary stor­age and solar folks, an inter­est­ing blend of envi­ron­men­tal­ists, prep­pers, and recy­clers try­ing to make bizarre franken­bat­ter­ies do their bid­ding. The safety pro­file is dif­fer­ent: they like LFP because they have a huge amount of energy stored in their house, but they also aren’t as con­cerned with the qual­ity of indi­vid­ual cell con­nec­tions because their bat­ter­ies rarely move.
• Flash­light enthu­si­asts. I haven’t spent too much time here, but for smaller packs, they could have some valu­able insight.

• Peo­ple who vape. Not my cup of tea. They’ve also some­how caused so many prob­lems that OEMs had to put explicit warn­ings on cell cases.

Future work

TodayApril 2025, I have just one bat­tery. But I have a lot of unused cells. I’m plan­ning:

• A bet­ter 3D printed case design for my cur­rent bat­tery to avoid hav­ing to use tape in any struc­tural way.
• A soft­ware appli­ca­tion to auto­mat­i­cally pro­duce a suit­able 3D printed case given a desired pack lay­out.
• A stor­age-ori­ented bat­tery, pos­si­bly con­nected to solar pan­els.
• An upgrade to my kWeld to use a sec­ond kCap mod­ule.