[also see [[electrical:12v:self-jumpstarting|self-jumpstarting]]]

===== maintaining starter batteries =====

  * Some [[electrical:12v:b2b#examples_-_combo_with_solar_charge_controller|combo DC-DC chargers]] contain logic to maintain the starter battery when solar power is present.
  * the [[https://amzn.to/40WMp2L|Bluetti 800w alternator charger]] (DC-DC) has a starter battery maintenance function.
  * Some standalone [[electrical:solar:charge_controller|solar charge controllers]] like the [[https://amzn.to/2PPTD2L|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. 
  * [[electrical:12v:alternator#voltage-sensing_relays|dVSR isolators]] (including [[electrical:12v:alternator#lithium-specific_vsr|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 [[https://battlebornbatteries.com/product/wakespeed-48v-12v-bi-directional-dc-dc-converter/|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 [[http://www.lslproducts.net/|apparently out of business]].
  * The [[https://amzn.to/47HMMyn|Xantrex echo charge]] maintains the chassis battery at up to 15A.


Experimental:  RV With Tito has [[https://www.youtube.com/watch?v=exQSsTiclOo|uses a PWM solar charge controller to maintain starter battery from the house bank]].  

Also see [[electrical:12v:alternator#gotchas|the subarticle on combiner gotchas]].

==== starter battery chargers alongside DC-DC chargers ====

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.

  - starter battery at 12.7v before charging applied
  - starter battery voltage rises from 10A charging
  - DC-DC sees >13.4v and [[electrical:12v:b2b#sizing|starts pulling ~22A]] to charge house battery at 20A
  - starter battery drops to 12.6v and DC-DC charger stops
   - 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 instead((for DC-DC models with starter battery maintenance, see above))