Deltran Battery Tender USB Charger From  €22.46

I've used this a couple of times now in conjunction with the 'Deltran Battery Tender Fused Ring Terminal Quick Connect'and it works absolutely fine. I haven't measured the drain on the battery but, when I go off camping, I charge my mobile phone up as soon as I can, rather than let its battery run very low. Consequently, I usually have the phone plugged in (and switched off) for an hour or less.