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Solar Charger for Discovery Auxiliary Battery

Posted by in Ask Bill, Solar Lights and Chargers on Apr 20, 2020 . .

Customer question (received via email 16th April 2020):

Hi Bill,

A bit of advice please, I have a Landrover Disco 3 running two batteries, main car battery and an Optima Yellow Top aux battery. In everyday use they are run with a split-charge system. The Optima gets little use for most of the year and most of the time does not get much chance to fully charge. I am looking to fit a Solar charging system for the Optima, What would you recommend?

The Optima is rated at 55 Ah (C20) 50 Ah (C5).

Many thanks


Willgen Reply (Email from Bill 16th April 2020):


Hi Mike,

Many thanks for getting in touch.

I would recommend either an Optimate 10 or Optimate 20 Solar Charger. The 10W panel if mounted outside in a South facing un-shaded position will be sufficient to keep the 55Ah (12V AGM) Optima battery topped up throughout the year (i.e charging Ah will exceed natural battery drain Ah throughout the year including mid-winter in UK). If the solar panel is going to be mounted in a less than ideal position (for example: flat on roof of vehicle, or behind windscreen glass) I would recommend an Optimate 20 solar charger.

If you want to recharge the aux battery with solar from a drained state (eg after use) you may want to consider one of the larger Optimate panels (40W, 60W or 80W) to speed up the charging process. The 10W and 20W versions will still charge a very depleted battery but will obviously take longer to recharge it than a larger solar panel. Often practicalities of space and where to the mount the panel prohibit the larger panels.

The Optimate chargers come with a charge controller that allows the solar panels to charge the battery even in low light conditions and will prevent battery damage through overcharging by regulating when the battery is fully charged. The charge controller also shows charging status when sunlight is sufficient to allow charging to happen and battery state of charge when there is no sunlight.

Note that all of the Optimate solar panels are fully weather proof and can be mounted permanently outside. The charge controller, although splash proof should be mounted undercover.

Links to products of interest:

Optimate 10:
Optimate 20:
4.6m Extension Cable:
Suction Cups:

Each solar charger is supplied with a weatherproof battery lead (with ring terminal connectors for permanent battery connection - but easy to connect & disconnect with plug and socket included) and a battery clamp lead (crocodile clips for temporary battery connection). In addition, there are a wide range of compatible accessories available on our website to aid installation and connectivity of the Optimate solar chargers.

I hope that this helps. Please get in touch of you have any questions or go to our website to place an order. All Optimate products are presently in stock and available for rapid despatch on receipt of order.

Kind regards


Last update: Jun 12, 2020
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