On 2/5/2020 8:57 AM, wrote:
Is there any danger of fire when charging lithium batteries? Is it O K to leave the charger hooked up overnight in an enclosed garage? It would be a 12 volt lawnmower battery. Thanks for a reply. Herb


Yes, unless you're using the manufacturer's charger that came with the
batteries. Otherwise read below from https://www.powerstream.com/li.htm



These remarks apply equally to lithium ion and lithium polymer
batteries. The chemistry is basically the same for the two types of
batteries, so charging methods for lithium polymer batteries can be used
for lithium-ion batteries.
Charging lithium iron phosphate 3.2 volt cells is identical, but the
constant voltage phase is limited to 3.65 volts.

The lithium ion battery is easy to charge. Charging safely is a more
difficult. The basic algorithm is to charge at constant current (0.2 C
to 0.7 C depending on manufacturer) until the battery reaches 4.2 Vpc
(volts per cell), and hold the voltage at 4.2 volts until the charge
current has dropped to 10% of the initial charge rate. The termination
condition is the drop in charge current to 10%. The top charging voltage
and the termination current varies slightly with the manufacturer.

However, a charge timer should be included for safety.

The charge cannot be terminated on a voltage. The capacity reached at
4.2 Volts per cell is only 40 to 70% of full capacity unless charged
very slowly. For this reason you need to continue to charge until the
current drops, and to terminate on the low current.

It is important to note that trickle charging is not acceptable for
lithium batteries. The Li-ion chemistry cannot accept an overcharge
without causing damage to the cell, possibly plating out lithium metal
and becoming hazardous.

Float charging, however, is a useful option. The safety issue with
keeping the battery on constant charge is that if the charger should
somehow go haywire and apply a higher voltage there could be problems.
And, so the logic goes, the shorter the charger is turned on the less
likely the charge will go haywire while connected to the battery.
However, there is another safety method, the battery protection board,
which should be included either on the battery or in other circuitry
between the battery and the charger. The BPB (also known as PCB for
"protection circuit board") or other battery management circuit will
stop the charge if the voltage gets too high.