I have this battery from eBay - http://www.ebay.co.uk/itm/171634446556
It is a POWER-TECH 850mAH 33C 2S 7.4V LI-PO Battery with JST Plug. The only thing is that it has two sets of wires. One + and - with a plug that is a JST but doesn't quite fit the Espruino, I assume I'll need to change this, but it also has another connector with 2 - and 1 + wire. Can I ignore this one and charge/discharge from the two wired connector?
The 3 wire one is for balance charging.
You can definitely discharge, and you should be able to charge it using the 2-wire connector (it will charge/discharge them in series), unless the manufacturer specifically went out of their way to prevent it from being charged like that. Try it and see... carefully, of course - if you have a current limiting power supply, I'd try putting the current limit way down, hooking it up to the battery, and ramping voltage up, and see if it starts charging.
You should charge it using a balancing charger at least once to make sure both batteries are in the same state of charge when you start dis/charging it through the 2-wire connector.
The JST plug of course doesn't match the Espruino one - "You are looking at a maze of funny little connectors, all different". JST is a company. Unfortunately, the name of the company, the letters in the part number, the numbers in the part number, and the number of conductors, all seem to get mixed up at random when people sell funny little connectors like this. I think the first try success rate on buying a connector that matches the Espruino is less than 50%. It's a JST PH series connector with 2 conductors. I think I got matching connectors on my third or fourth buy.
...the plain things bring a high tech endeavor down... such as not having the right plug, or not plugging in, or... you name it.
There's a list of places to buy Espruino's JST connector right here. Apart from one issue of Makersify accidentally sending out the wrong part, I think all those links are correct.
I'd consider buying the other end of the battery connector and making yourself an adaptor (rather than hacking your battery around). I think the other end is this one
Just a note about charging - Espruino won't charge batteries (The rev 1v4 board has a place where you can solder a charger IC though). But, like the small USB-powered LiPo chargers you can get, it's meant to charge a single LiPo cell (not the two cells in that battery pack).
To charge it your best bet is to use something like this - it'll come in handy for all sorts of other stuff too!
Thanks for the advice guys, I already have one of the recommended small USB-powered LiPo chargers, so I may just buy a new battery, I'll check out the balanced chargers also.
If you get JST connectors (digitalmeans do them very cheaply) then you may be able to use some batteries you have kicking around...
Old phone batteries work great, and you can also salvage cells from old laptop batteries (although you want to be careful as those ones don't have protection circuitry in each cell).
I took your advice, I now have a packet of these connectors and a couple of batteries from my Galaxy S4.
The ratings are 3.8v and 2600mAh, they have 4 connection points with + and - marked, but I don't know what the other 2 are for. Do I charge and discharge from the same connectors or is there something else I need to do?
Pins 1 and 3 are the ones you want, it looks like - that's what other people seem to use.
I suspect the other two are used for some means of monitoring battery state.
@DrAzzy I wired up those pins and I have power! My board is now free from the shackles of the USB lead, thanks for your help.
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