Originally Posted by
moetorola
Yes, the both batteries voltage wise would be at some voltage since they are parallel but not necessarily capacity wise.
Batteries of different age, manufacture date for a few examples. It is never a good idea to charge two 12volt batteries the are in parallel. They should be monitored separately.
While the voltage may be the same one battery may reach 100% charge while the other is at 80%. Or vise versa, while one battery has reached 100% the other 80% the charger may over charge the fully charged battery. It really depends on charger being used at the end of the day. The old cheap metal style chargers with no regulation voltage based charging only, I would not trust em.
It is frowned upon in the industry I work in. When in nearly every case the batteries are left unattended and some cases forgotten about. This method may be fine for charging up, but for float charging long term, as most of us do today, not recommended.
Luckily with todays chargers having individual banks, each battery is monitored separately we don't have to worry about this. Except in parallel.