I had the same problem as you until I bought a Battery Tender. Also, check the electrolyte level periodically and top up with distilled water. The 300CCA battery is better. Keep your terminals clean. Yes, U1 batteries are basically all the same. The CCAs May be different.So all these batteries are basically the same, just more money for the name brands?
Correct! And that is why some of them have internal heating elements that their intelligent battery management systems will divert charge power to until they are safe to charge. Note that there is no danger in discharging them below 32 F, meaning that you can start your equipment and then warm the battery until it can safely charge. Such features are presently available on the larger solar storage batteries. Just about anything with a battery management system will prevent charging below the minimum temperature.The main problem with LiFePO4 batteries is that they will be destroyed if charged below 32f.