It it safe to wire up 2x 20v cordless batteries in series to make 40V?

[TigerUK]

Hello

I had my eye on this cordless pressure washer for a long time. I moved from a house to a flat and want a pressure washer to wash my car.

https://greenworkstools.eu/global/en/ga ... hers/gdc40

I dont want to buy their battery because it's expensive and it's a big powerful battery pack - i dont want to leave it unused, discharge buy itself and cause a fire risk.

LI-ion battries should be used regularly so they are no stored at full capacity or on low capacity for too long.

I also have loads of 20V parkside batteries.

I was wondering if it's possible to connect two batteries in series or is that potentally dangerous?

They sell empty shells of the greenworks battery here: https://www.ebay.co.uk/itm/363577155782, I could buy one of them - or someone selling a dead battery for the interface to convert to 2x 20V adapter.

I dont trust generic brand batteries - espeically not big ones that are 4Ah 40V. So those cheaper ones are no-go. Besides I really dont want to buy a battery that will be left unused for a month at a time.

[kellys_eye]

You don't want to buy 'their' battery because it's dangerous yet you want to make your OWN that isn't???

Do you know that Greenside battery watt/hour rating? It's probably exactly the same as what you intend to make but without the danger! Besides, if you get it wrong your pressure washer probably won't work for very long.

The batteries (either Parkside or Greenworks) probably use 18650 type cells anyway so the actual capacity will depend on the version you purchase - some can hold more energy than others (more expensive).

[Someone-Else]

FYI: A battery is made from a number of cells (Depending on voltage) in most cases the cells are connected in series.

The thing you link to is NOT made to accept two batteries, it is made to accept the cells from those batteries*. Are you confident in taking the batteries you do have apart to get the cells out?

*Look at the 4th picture, you can clearly see the + and - symbols telling you which way up the cells should go, and there is also a bag of metal bits to connect one cell to the next. Presumably instructions too.

[big-all]

lithium-ion batteries are dangerous things if you get it wrong or bypass the safety circuits you can easilly have a flame thrower on your hands
look up "run away lithium ion batteries"
or "lithium ion batteries catch fire"
or any combination off "fire" and" lithium" in the same sentence

[kellys_eye]

lithium-ion batteries are dangerous things if you get it wrong or bypass the safety circuits

Which is also why the official manufactured batteries are the safest way to go. The manufacturers are aware of the potential for litigation if they allow their batteries to cause harm, damage or destruction etc so they'll be designed and built with all the appropriate safety in mind - safety that an individual might conceivably not fit or get right if they made their own.