In article ,
Chris Green writes:
"Dave Plowman (News)" wrote:
In article ,
Chris Green wrote:
David wrote:

It is a few years old and doesn't match the new one in the caravan so
just linking the two together may not be the best option.

If they're both the same technology (i.e. lead acid, liquid
electrolyte - or - lead acid, gel - or - whatever) then I don't really
see any problem with simply parallelling them to get the 'extra' one
charged. It would probably be worth disconnecting it if leaving long
term.

You need well above the nominal battery voltage to charge it fully.

Er, yes, there is presumably something charging the 'first' battery so
it will charge the added parallel one as well.

IME, cigar lighter sockets are hopeless for long duration
current rating (anything over a couple of amps). The contact
resistance is too high and they overheat, because they don't
have contacts with large enough surface contact and high
enough pressure.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]