Update: The original Harbor Freight battery failed to start my Eldorado after sitting unconnected in winter for nearly 2 months, so I replaced it with another one from the same model jumpstarter, bought recently for less than $40 on sale. It had the same battery markings as the the previous one. I got nearly 3 years service out of it, often letting it sit for months while away on work assignments in the temperature extremes that occur in the southwest, it was never babied and rarely put on a Battery Tender or charger.
Suddenly the bike needs a new battery. There are lots of options out there, but it happens at a time when I want to use the bike, which means this is about taking advantage of local retail economics. A new 18ah MC battery at the auto parts chains is typically $100 for a SLA (Sealed Lead-Acid).
Or you can go to Harbor Freight and buy an automotive jumpstarter for $40-60 (search for coupons) that has a similar battery inside. These often include a tiny air compressor that can be removed and wired to work with your battery tender leads or other 12v accessory plugs.
The HF jumpstarter battery I’m using is a 17ah, and has lasted through over 2 years of wide temperature variations, long periods of storage, a formerly feeble charging system, and rare Battery Tending, yet still cranks my Eldorado reliably. It is much more lively since the alternator conversion described on a another page here. It came in the lowest-end jumpstarter, on sale for $33 in 2010. Included, because of it’s intended use, is a charger purpose-built for that battery, AC cord, Voltage meter, 12v light, and 2 short jumper cables, a heavy-duty 12v switch…if you like to scavenge and make things from parts these are a great value.
In the interest of economic science, I took apart a jumpstarter I bought from Costco, which runs about $70. It comes with a battery about the same size, but rated 18ah. I actually use that one for work projects, so it got put back together. The second photo shows the small compressor which could be removed and used as an on-board inflator.