En 
SvWhich batteries should I buy?
Lead-acid batteries
Economically speaking, you should get the most ampere-hours per crown with standard marine or leisure batteries from well-known manufacturers such as Exide, Varta and Global. They are normally 75 – 80 Ah. If you buy larger lead-acid batteries, they are more expensive per ampere-hour, and they are much heavier and more difficult to get into the boat.
In addition to starter batteries, there are leisure batteries and various specialised batteries such as gel and AGM batteries.
A starter battery is made for quick discharges and charges, but is poor for deep discharges. The leisure battery is designed to withstand deeper discharges, down to 45-50 per cent of the battery’s capacity at the expense of starting current capacity in severe cold. A standard marine battery has a starting current of over 500 A already at -30°C. This is enough to start the vast majority of engines.
Gel & AGM batteries
Gel and AGM batteries can withstand even deeper discharges and more cycles, but they are more expensive batteries. However, you get more Wh (watt-hours) out of such a battery. So the cost per Wh you can use won’t be that much higher, in some cases it might even be cheaper with an AGM or Gel battery.
You usually don’t need a special starter battery, but can have lead batteries of the same type throughout the battery bank. Then you can also switch so that the starter battery, which never gets deeply discharged, can become the consumer battery after a season. This way you extend the life of your batteries.
Lithium batteries
Lithium batteries are a staple in your mobile phone and are slowly but surely making their way into vehicles. If you are looking at specialised lead batteries, you should consider getting lithium batteries. The price difference is smaller than in the past and the quality of lithium batteries is now really good.
There are different types of lithium batteries.
Lithium-polymer batteries are the ones used in mobile phones. They are expensive, have high capacity and are suitable for small compact batteries.
Lithium-ion is found in hand tools, for example. They require constant monitoring as overheating can cause explosive collapses.
The third type is lithium iron phosphate batteries. They have a slightly lower energy density than the other two, but are chemically more stable. These are the most suitable for use in boats, motorhomes, caravans, etc.
A lithium battery weighs less than half as much as an equivalent gel battery and takes up about half the space. But the big advantage is the charging capability.
