Batteries. AGM technology is the way forward. Calcium batteries need to be avoided. Albeit ok in a daily driver with low loads, if they are run below 12 volts for more than 12 hours then they tend to never recover properly.
Unsure of your battery, a rough guide to it's effectivenes is to trickle charge it over night, let it settle for a couple of hours then turn the headlights on for 10 seconds, turn them off and measure the float voltage. Should be between 12.53 and 12.74 on a good battery.
Hellfrauds batteries are not very good quality and have a low plate count per cell.
I've stuck a clodding great Varta AGM in mine. Exide, Varta and Bosch are all good brands as well and tend to work well. Hoppecke can be good value for money but they are Bosch seconds. Gel batteries such as yellow top optimas are good but don't last. If you want advice on the ultimate batteries join a Car Audio forum like talk audio and speak to the SPL guys.