I can source an AC Delco LN1 for about $140 but I decided to use my Spark as guinea pig for future battery replacements in my other vehicles. My total cost was about $80 (60 + 15 + 5). If I need to replace the battery I don't need to make another bracket nor get another set of terminals, both of those can get reused. I also added a $10 heatshield as the underhood temps and the stock battery felt really warm after normal use.
I would say a substantial amount of motorcycle batteries are AGM so they're extremely easy to source, also since the 12V in the Spark never really cranks an engine switching to a motorcycle sized AGM shouldn't really be worked hard. I used a Chrome Battery 30L-BS AGM battery, it was about $60 from Amazon, which is a substantial savings over any automotive AGM battery. I prefer Chrome because they have a 18 month warranty and their customer service is based in the USA. You can use whatever battery brand you like, IMO all the ones at this price point are coming out of the same place in China.
A little info on motorcycle battery sizes: https://www.batteriesinaflash.com/motor ... -reference Pretty much the higher numerical value means a physically bigger battery, BS/BL refers to the orientation of the positive terminal on the battery.
To do this mod you need to buy 2 things in addition to the battery:
- SAE Terminal adapters https://www.ebay.com/itm/264571832112
- Make your own battery mounting bracket, I used aluminum stock from Home Depot/Lowes/ACE
- Optional, some thermo barrier to decrease battery temps and prolong life. Search for "Hook and Loop heatshield", i used this https://www.amazon.com/gp/product/B08JKN1LYH/