I may be able to add more batteries if I put sealed lead acid batteries on side or upside down, is this safe??? I could put each battery in baggie to help.
Usually they are OK upright or on their side, but not upside down, as there is a small risk that the over-pressure vent may not work properly if they are mounted this way. Most sealed and AGM lead acid batteries have clear instructions on mounting. For ebike use they aren't great performers, but they are cheap in the short term (but expensive in the long term, due to their short life).