# Charge both batteries **URL:** \ **Category:** DIY\ **Tags:** mppt, rv, cyrix\_battery\_combin, beginner\ **Created:** [18 March 2025 08:54 UTC](https://community.victronenergy.com/t/charge-both-batteries/25606 "2025-03-18T08:54:07Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![Hoff](https://avatars.discourse-cdn.com/v4/letter/h/ce73a5/32.png) [@Hoff](https://community.victronenergy.com/u/Hoff)\ **Post date:** [18 March 2025 08:54 UTC](https://community.victronenergy.com/t/charge-both-batteries/25606/1 "2025-03-18T08:54:07Z")
Question: I have a campervan with a Schaudt Booster WA 121525 installed. Which charges the consumer battery when the engine is started. I know absolutely nothing about this product. I have a Victron SmartSolar 75/15 MPPT connected directly to my consumer battery. Is it possible via a Cyrix-ct battery combination kit to get the MPPT charger to charge the starter battery when the consumer battery is fully charged? Or will it create a kind of loop when the engine is on and the booster is activated? ---
**Author:** ![pwfarnell](https://dub1.discourse-cdn.com/victron/user_avatar/community.victronenergy.com/pwfarnell/32/2341_2.png) [@pwfarnell](https://community.victronenergy.com/u/pwfarnell)\ **Post date:** [18 March 2025 10:24 UTC](https://community.victronenergy.com/t/charge-both-batteries/25606/2 "2025-03-18T10:24:39Z")
If you connect with a Cyrix then when the consumer battery is being charged from any source, the Cyrix will connect the batteries together, which will bypass whatever charge circuit is in the Schaudt Booster. I have no idea if this is a problem or not. It could result in cycling if the consumer battery voltage then fell and the Cyrix disconnected or unregulated charging if the engine battery is at too high a voltage. A better idea may be a small trickle charger such as the one linked below. These have a diode in to prevent reverse current flow. You may get a bit of charge from the consumer to the engine battery when the engine is running but that is probably not an issue. > **[Votronic 12V StandBy Charger (DC-DC Trickle Charger)](https://www.12voltplanet.co.uk/votronic-12v-standby-charger-trickle-charger.html)** > > The Votronic StandBy Charger trickle charges your 12V starter battery whilst your 12V leisure battery is being charged from a mains charger or solar panel. ---
**Author:** ![Hoff](https://avatars.discourse-cdn.com/v4/letter/h/ce73a5/32.png) [@Hoff](https://community.victronenergy.com/u/Hoff)\ **Post date:** [18 March 2025 18:06 UTC](https://community.victronenergy.com/t/charge-both-batteries/25606/3 "2025-03-18T18:06:39Z")
Unfortunately, that won’t work because that setup doesn’t share the negative connection. ---
**Author:** ![Hoff](https://avatars.discourse-cdn.com/v4/letter/h/ce73a5/32.png) [@Hoff](https://community.victronenergy.com/u/Hoff)\ **Post date:** [19 March 2025 08:45 UTC](https://community.victronenergy.com/t/charge-both-batteries/25606/4 "2025-03-19T08:45:12Z")
What about Victron Smart BatteryProtect, would it be able to do the job? ---
**Author:** ![pwfarnell](https://dub1.discourse-cdn.com/victron/user_avatar/community.victronenergy.com/pwfarnell/32/2341_2.png) [@pwfarnell](https://community.victronenergy.com/u/pwfarnell)\ **Post date:** [19 March 2025 09:17 UTC](https://community.victronenergy.com/t/charge-both-batteries/25606/5 "2025-03-19T09:17:26Z")
No, Smart battery protect is just an electronic / solid state relay so has the same connection issues. Plus it can flow current both ways but it will be damaged by reverse flow. ---
**Author:** ![Hoff](https://avatars.discourse-cdn.com/v4/letter/h/ce73a5/32.png) [@Hoff](https://community.victronenergy.com/u/Hoff)\ **Post date:** [19 March 2025 09:32 UTC](https://community.victronenergy.com/t/charge-both-batteries/25606/6 "2025-03-19T09:32:00Z")
Maybe then the only way will be a Orion-Tr Smart DC-DC Charger Isolated? ---
**Author:** ![pwfarnell](https://dub1.discourse-cdn.com/victron/user_avatar/community.victronenergy.com/pwfarnell/32/2341_2.png) [@pwfarnell](https://community.victronenergy.com/u/pwfarnell)\ **Post date:** [19 March 2025 09:58 UTC](https://community.victronenergy.com/t/charge-both-batteries/25606/7 "2025-03-19T09:58:16Z")
That would definitely work with isolated systems. The other thing that would work would be to connect the solar to the engine battery and let the Schaudt Booster charge the consumer battery if it could detect the higher voltage from solar and turn on like a normal DC to DC charger. I do not know anything about it though. ---
**Author:** ![Hoff](https://avatars.discourse-cdn.com/v4/letter/h/ce73a5/32.png) [@Hoff](https://community.victronenergy.com/u/Hoff)\ **Post date:** [19 March 2025 10:05 UTC](https://community.victronenergy.com/t/charge-both-batteries/25606/8 "2025-03-19T10:05:40Z")
True, problem is that the booster only is on when the engine is turned on ass well. ---
**Author:** ![system](https://europe1.discourse-cdn.com/victron/original/1X/21a9a7b5db7c6339715f993568736a7053199995.png) [@system](https://community.victronenergy.com/u/system)\ **Post date:** [15 May 2025 20:04 UTC](https://community.victronenergy.com/t/charge-both-batteries/25606/9 "2025-05-15T20:04:28Z")
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