Choosing a Battery Charger

Unfortunately, many people spend good money on batteries, only to ruin them by using very basic car battery chargers, or finding that they take an age to charge because the charger is far too small. As a very basic guide, many cheap chargers on the market today only produce a 1A charging current, which would take somewhere in the region of 4-5 days to charge a flat 110Ah leisure battery.

As a result, we have chosen to supply only a range of semi-professional / professional 12V chargers, all of which are designed to work with large leisure batteries or banks, of AGM, lead-acid or gel types. Using the correct type and size charger will significantly extend the lifetime of leisure batteries, which can save you hundreds of pounds in the future.

When choosing the correct size of charger for your battery(ies), choose a charger that is typically about 10% of the total battery capacity in Ah, e.g. use a 10A charger with a 100Ah battery. To be more accurate with the size calculation, the starting point should be the required charging time. For adaptive chargers, take the total battery capacity in Ah and divide it by 2 (we recommend keeping batteries 50% charged at all times). Take 80% of this number and divide it by the output of the charger; the last 20% of the charging cycle will take half the time of the first 80%.

Example: 250Ah AGM battery
250 / 2 x 80% = 100 divided by 20 (for a 20A charger) = 5 hours x 1.5 = 7.5-hour total charge time.

Charging Time in Hours (from 50%)
Battery Size (Ah)
100
250
500
1000
10A charger
8
19
38
75
20A charger
4
9
19
38
30A charger
3
6
13
25
40A charger
2
5
9
19
50A charger
2
4
8
15
60A charger
1
3
6
13