• Some combo DC-DC chargers contain logic to maintain the starter battery when solar power is present.
• the Bluetti 800w alternator charger (DC-DC) has a starter battery maintenance function.
• Some standalone solar charge controllers like the Morningstar SunSaver Duo can, for example, charge the start battery with 10% of solar harvest and the house battery with 90% using different charging profiles. As with DC-DC above, it's not self-jumpstarting in the normal sense but can help prevent the dead starter battery.
• dVSR isolators (including the Li-BIM) automatically connect the banks when the voltage on either side reaches defined setpoints.
• Some Victron Multiplus models have a 4A starter battery maintenance feature.
• the BattleBorn/Wakespeed 48v/12v Bi-Directional DC-DC charger can maintain the starter battery voltage from the 48v house bank.

There are dedicated maintainers:

• Some RVs were equipped with original Trik-L-Start or lithium-compatible Amp-L-Start modules by LSL Products, which is apparently out of business.
• The Xantrex echo charge maintains the chassis battery at up to 15A.

Experimental: RV With Tito has uses a PWM solar charge controller to maintain starter battery from the house bank.

Also see the subarticle on combiner gotchas.

If a DC-DC is present and relatively weak shore power charging is applied to the starter battery there are circumstances where the DC-DC can cycle on-off constantly. Let's consider a 20A DC-DC and a 10A starter battery maintainer.

1. starter battery at 12.7v before charging applied
2. starter battery voltage rises from 10A charging
3. DC-DC sees >13.4v and starts pulling ~22A to charge house battery at 20A
4. starter battery drops to 12.6v and DC-DC charger stops
5. repeat forever

To avoid this scenario either:

• ensure the DC-DC rating is smaller than the starter battery rating; or
• apply the shore power charging to the house bank side instead¹⁾