I'm not sure how the G1 is set up. If you can upload pictures, that might help. If it's anything like the G2 I have, it's likely it uses 3 12v SLA batteries for a total of 36 volts. I would suggest you buy 100 amp hour batteries so you get a nice long run time. You'll want to measure the size of the battery (width, height, depth) so you make sure you buy batteries that fit in the battery box. In addition, if your batteries are like mine, they likely have M6 screw holes for terminals instead of what you typically see with a car which uses posts. Also make sure the SLA batteries you buy are deep cycle batteries. You definitely don't want to put car batteries in there because they won't give you much runtime.
On another note, I remember when the Rechargemower site still displayed the batteries and other accessories. The price they wanted for the batteries were quite high compared to what you can find on the internet for much cheaper. I'm fairly confident I could buy 3 new batteries for my G2 for around $500 right now. You know it's funny that the Rechargemower website is still up despite the company going bankrupt. I wonder who's paying to keep it up?
I didn't realize that my post had gotten replies. Thank you and sorry for the delay in responding.
I think the batteries for the G2 are larger, at least is seems that way from the images and prices on the Recharge site. the Recharge site price is also $799 for the G2 and $399 for the G1.
The battery for the G1 is listed 2 different ways. In the manual is it listed as a 12V 55ah and on line in the parts sections it is pictured with 12V 38ah on the battery. Unfortunately it doesn't list the dimensions so I would need to take it all apart to measure the batteries. I have been researching online today again for possible replacements. From your reply I take it that one can replace the batteries with higher amp hours. I didn't realize that. That changes the possibilities for the better. I don't know what is actually in the mower (38ah or 55ah) since I haven't dismantled it yet and am waiting for the mowing season to be over. This year and last, I managed by using it 15 minutes at a time and recharging. When the mowing season is over I will take it apart so that I can measure the batteries. I've attached images supporting the battery information that I have from the Recharge site and the G1 manual (first time doing this, so hope I did it correctly). The thumbnails are showing the images as being the same in the preview, but they are actually 2 different images when you click on them.
I also just learned today what the terminals on my batteries are called, i.e., insert terminals, which according the images on the site are the same on both models.
I'd also like to find a source for replacing the blades. But again there are no specifics about the blades except for the photo. The G1 blades cost less, and I know that the G2 is a bigger mower so most likely the blades are not the same size.
So onward with the problem solving.
Thanks for your input.
