Ryobi P640K Manuel D'utilisation page 5

 Do not charge battery tool in a damp or wet
location. Following this rule will reduce the risk of electric
shock.
 For best results, your battery tool should be charged
in a location where the temperature is more than
50°F but less than 100°F. To reduce the risk of serious
personal injury, do not store outside or in vehicles.
SPECIFIC SAFETY RULES
5 — English
 Under extreme usage or temperature conditions,
battery leakage may occur. If liquid comes in contact
with your skin, wash immediately with soap and water.
If liquid gets into your eyes, flush them with clean
water for at least 10 minutes, then seek immediate
medical attention. Following this rule will reduce the risk
of serious personal injury.