Unrelated very beautiful picture of beer, which I do not drink.

I have a 80 AH deep cycle battery that I take camping with me to power my CPAP machine at night. I recharge the battery the next day by various means. This week, I’ve lent the battery to a friend who also sleeps with a CPAP. I’d like to pick up another deep cycle battery with greater capacity and keep both of them around for provident purposes.

Two questions: If you ganged the reds and the blacks together — parallel, right? — could you charge them at the same time?

Also: given your expertise, what do you think of this offer on Craigslist? Guy says the batteries are five years old.

Thanks!