Ryobi 36v Batteries are not Waterproof.
I bought a 36v Ryobi lawn mower as a gift last year - works really well.
Went to the house where the mower now lives and noticed the 5Ah battery sitting on a wet chair outside - yep the battery had been left out in the rain for a few days and was now dead [bigsad] with water pouring out of it.
I investigated and tried all the recommended ways to resurrect the battery, all to no avail. The management system has a circuit to stop over charging and a separate circuit that shuts the battery down if voltage drops to just over 30v - hence the appliance does not slowly run down when battery runs down but just stops. If the battery drops below 30v it will not charge so other means are needed to to get it above 30v so the charger will charge.
I bypassed the management system in the battery and the voltage at the battery was only 15v so a few cells have dropped. Put 38v to just the battery and it go to 22v but when power removed drops straight back to 15v. Not sure if the BMS is also gone.
Now while I bought this mower it is not actually mine and Bunnings wants $299 for a new 6Ah or 2x 4Ah batteries. If the owner wants Ryobi batteries he can buy his own - but I did spring for a 6Ah no name battery from ebay for $130. No great expectations but I have a couple of knockoffs myself and they seem OK.
Now the Ryobi 5Ah battery weighs 1.4kg and the 6Ah ebay special only weighs 1.2Kg so probably is only about 4Ah - low expectations achieved. Ryobi tends to use middle of the range LG batteries, though sometimes you might get Samsung so nothing special. The knockoffs are usually cheap low performance no name Chinese batteries hence the lighter weight.
The actual performance of the knockoffs vs cost is not so bad, the real issue is just their claims - claimed to be a 6Ah but probably about 4Ah - still a lot cheaper than Ryobi but is definitely not as advertised.
I am going to remove the circuit board of the Ryobi and find out how many of the cells have failed and see if putting new ones in brings the battery back.
garry