John,
During the lunar eclipse 2 weeks ago, I ran my Takahashi EM-200 (EQ6 clone) from an 8 year old 12v 7AH SLA battery from 630pm to just after midnight.
This one is 12V 9AH and quite cheap, you could buy two, have one in reserve or connect them in parallel. They are only a couple of kilos each.
https://www.sunyee.com.au/products/m...SABEgK94vD_BwE
You'll also need a charger to suit and and adaptor to clip on to make it a cigarette lighter socket.
I made one from a socket, 4 cables and 4 spade lugs wired so that if I want more power for other accessories, I can connect two of these 7AH batteries in parallel but as I mentioned, one of these ran my EQ6 clone with two scopes in a DSBS saddle plate for 5.5 hrs without batting an eyelid. i know it's not as sexy as lithium but it's a fraction of the price. Looked after they last for years.
Joe