Gutt100 Posted May 13, 2021 Share Posted May 13, 2021 Hi, New to this so please excuse the question if very simple *-) My motorhome has two leisure batteries which are connected together and my control panel was showing leisure battery poor 4.5V When i disconnected the batteries and placed on charge one was very low on charge but the other showing 95% according to my Numax charger? Should the two batteries not work in tandem or am i missing something simple? Thanks Link to comment Share on other sites More sharing options...
Keithl Posted May 13, 2021 Share Posted May 13, 2021 It sounds as though one of your batteries has failed. Disconnect both batteries and then let them rest for at least an hour, then measure the voltage across the terminals. Report back with the figures please. Keith. Link to comment Share on other sites More sharing options...
Gutt100 Posted May 13, 2021 Author Share Posted May 13, 2021 Hi Keith, I have the low battery on charge now. My question was more towards why one battery would be low and the other high when they are wired together. I maybe naively assumed that two batteries would balance each other out or one would run down and then the second take over? Thanks Paul Link to comment Share on other sites More sharing options...
mikefitz Posted May 13, 2021 Share Posted May 13, 2021 Hi Paul. Batteries have a finite life and may age differently for many reasons, such as production tolerances or even the way they are connected in circuit. My advice would be to replace both. If they have been at at the low voltage of 4.5 volts for some time, then both will be damaged. Your charger is only capable of measuring voltage and cannot measure the capacity of the battery. Its quite possible a nominal 100Ah battery will show a satisfactory voltage but only have a capacity of a few amp hours. Lead acid batteries should be regarded as consumables, and typical 'leisure' batteries together with the often inadequate motor home charging systems, do not have a long life. Mike Link to comment Share on other sites More sharing options...
Derek Uzzell Posted May 14, 2021 Share Posted May 14, 2021 Some light reading... https://batteryguy.com/kb/knowledge-base/connecting-batteries-in-parallel/ https://www.garagejournal.com/forum/showthread.php?t=88572 https://www.quora.com/What-happen-when-a-dead-battery-and-a-good-battery-connected-in-parallel Link to comment Share on other sites More sharing options...
rayc Posted May 14, 2021 Share Posted May 14, 2021 Gutt100 - 2021-05-13 2:46 PM Hi Keith, I have the low battery on charge now. My question was more towards why one battery would be low and the other high when they are wired together. I maybe naively assumed that two batteries would balance each other out or one would run down and then the second take over? Thanks Paul Perhaps your battery paralleling cable and connectors are faulty in some way and in practice only one of the batteries is actually connected? do not think this cannot happen. A friend had a dealer fit second battery fitted to his new motorhome. The battery connectors to the second battery were loose in their clamps and the battery was doing nothing. What voltage readings do you get at each battery positive and negative battery terminals when they are connected together? If both batteries are not showing the same then there is a problem with the cables / clamps. When batteries are connected in parallel they should both share the load and discharge together. One does not discharge and the other take over. Link to comment Share on other sites More sharing options...
Brian Kirby Posted May 14, 2021 Share Posted May 14, 2021 Gutt100 - 2021-05-13 10:45 AM Hi, New to this so please excuse the question if very simple *-) My motorhome has two leisure batteries which are connected together and my control panel was showing leisure battery poor 4.5V When i disconnected the batteries and placed on charge one was very low on charge but the other showing 95% according to my Numax charger? Should the two batteries not work in tandem or am i missing something simple? Thanks But, for the batteries to work as a pair, they must be a pair. That is to say, same make, type, chemistry, ideally capacity, and above all, age. If any of the above are not the case, one will dominate to the detriment of the other. On a 2005 van it is extremely unlikely that either is an original, so it is quite possible that some past owner has either added a battery to an already existing battery, so that even if superficially identical their ages are significantly different, or has added a non-identical battery so further compounding the mis-match. The best advice, as above, would be to replace both with a matched pair, being mindful of the charging regime of your on-board charger, and of whether it is capable of being adjusted to an optimal regime for different battery types. If you can identify your van's on-board charger as fully as possible, someone will probably be able to advise its capabilities and limitations, and consequently the best type of battery to suit its characteristics. Just be aware this may get a bit "techy" - batteries are a notoriously complex subject! :-) Final thought: I assume your present batteries both have vent tubes running from them to external air? A good source of batteries is the on-line retailer Tayna, here: https://www.tayna.co.uk/leisure-batteries/ Good, informative website, and large turnover that reasonably assures the batteries will not have been standing around gently deteriorating before you fit them. Where leisure batteries are concerned, be very cautious of buying stock from local supply sources, as their turnover is liable to be low and you may well be offered batteries that are, due to the time they have spent on the shelf, already well past their prime. If the supplier has to get them in rather then supplying from stock that risk is reduced - providing in turn their supplier has fresh stock that has been properly stored. Link to comment Share on other sites More sharing options...
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