The battery needs a full charge and cool-down before it can be tested properly. If you have a good charger at home you can charge it then take it in for the test.
The best tenders on the market hands down are the line up from CTEK. Depending on the battery you have (lead acid, AGM, lithium, etc..) they have numerous chargers out there for each style and your requirements. If it is an AGM or conventional battery, grab the CTEK 4.3, grab some extra bolt on pig tails for your battery and go to town. I even use a 10ft CTEK extension to run my charger on concrete and hang the terminal out of the hood, no popping hood to get a charge, just pull in garage, plug in and walk away. the 4.3 shows you what "step" it is working on and will tell you have your battery is 100% junk as it can tell when it is not taking the charge. They sell a 0.8amp too, no buttons, low heat, plug in and walk away no options to pick, but not the best for AGM batteries.
