This innovative device from Ring Automotive provides ‘clean, green and free energy’ wherever you are. The RSP150 model is suitable for batteries up to 50Ah.

Realistically you will need to purchase the more powerful RSP240 or RSP480 to charge a towcar or leisure battery but it does enough to provide a trickle charge and will replace what is taken by a radio memory or alarm system.

To test its charge, however, the smallest one performed brilliantly and only produced 1A less when it was behind a windscreen than when it was outside. All models come with suction-cup or screw-in fixings, and can be charged via your car’s 12V socket.

Also supplied are battery connectors and full instructions for bringing your motor back to life. The next time you turn the key to find a drained battery, the battery maintainer could be the difference between eating your food flambé or positively al dente.

If you find that there is too little sunshine in your favourite caravan holiday locations to power solar devices such as this, you might be better off buying a smart modern battery charger. Practical Caravan’s test of eight rival battery chargers in late 2014 takes a comprehensive look at the Ring SmartCharge+ 12, Ring SmartChargePro 25, CTEK MXS 7.0 charger, CTEK MXS 5.0 charger, Sealey Autocharge 10D, Draper 11953 battery charger , Draper 07265 battery charger and finally the Clarke CC120 battery charger