Electrical and Systems
Auxiliary Battery Banks and DC-DC Charging for Vans and Fleet Vehicles
Typical range
$750 to $7,500
Shop hours
4 to 30
Labor rate
$260/hr
The short answer
Auxiliary battery and DC-DC charging work builds a second bank that charges from the engine alternator without damaging it, using a current limited DC-DC charger instead of a simple isolator. Work runs $750 to $7,500, or 4 to 30 hours at $260 per hour plus equipment.
01
What this work actually involves
A traditional battery isolator connects the house bank to the alternator through a relay and hopes for the best. That was acceptable when house banks were two lead acid batteries that tapered charge current on their own. It is not acceptable with lithium, which will accept everything the alternator can produce and hold it there. Modern Sprinter, Transit, and ProMaster alternators are also temperature regulated by the engine computer and are not designed for sustained full output, so a lithium bank on a plain isolator will cook an alternator that costs more than the batteries did.
A DC-DC charger solves both problems. It limits the current drawn from the alternator to a set value, and it delivers a proper multi-stage charge profile to the house chemistry regardless of what the alternator bus is doing. On smart alternator vehicles that drop to 12.4 volts under regenerative strategies, a DC-DC unit boosts the input up to a real charge voltage, which a simple isolator cannot do. This is the single most common thing missing from van conversions that come to us with a house bank that never fills on a driving day.
The install detail that matters is cable and fusing. The run from the engine bay to the house bank in a Sprinter or a Class C is long, and the voltage drop over that run determines how much charge you actually get. We size for the drop, fuse at both ends near the source, protect the cable at every body pass-through, and add a battery monitor with a shunt so you can see what the system is really doing instead of guessing from a voltage display.
Systems and brands we work on: Victron, Battle Born, LiFePO4, AGM, Xantrex, Magnum.
Location: All work is performed at our Yorba Linda facility. We do not offer mobile, roadside, or fleet route service.
02
What the job includes
- Auxiliary house bank design, sizing, and mounting in vans and fleet vehicles
- DC-DC charger selection, installation, and current limit programming
- Smart alternator and variable voltage vehicle compatibility evaluation
- Alternator output capacity assessment before adding charge load
- Long run cable sizing to measured voltage drop with fusing at both ends
- Body pass-through grommets, chafe protection, and secured routing
- Battery monitor and shunt installation with correct capacity programming
- Integration with solar charging so the sources coordinate rather than conflict
- Bank isolation so the starting battery is never drawn down by house loads
- Fleet upfit power for equipment, refrigeration, and medical or workshop loads
03
When you need this service
- House bank barely gains charge after a full day of driving
- Starting battery goes flat while the house bank still shows capacity
- Alternator running hot, whining, or failing repeatedly after a lithium upgrade
- A lithium bank connected through an old style isolator relay
- Voltage at the house bank reads well below alternator output voltage
- Equipment in a work vehicle shutting down before the shift ends
04
How we do it, step by step
- 01
Vehicle charging system assessment
Alternator rating, regulation strategy, and existing bus voltage measured while running. Smart alternator vehicles behave very differently and the plan depends on which you have.
- 02
Load and capacity calculation
Daily consumption totaled against driving hours so the bank and the charger are sized to actually replace what you use, not to a round number.
- 03
Charger sizing against alternator headroom
DC-DC current limit set below what the alternator can sustain with the vehicle at idle in traffic, which is the worst case that kills alternators.
- 04
Cable run and protection
Cable sized to the measured run length and drop, fused within inches of each source, and routed with grommets and loom through every body pass-through.
- 05
Install and program
Bank, charger, and shunt installed, charge profile matched to chemistry, and the ignition or voltage sense trigger configured for your driving pattern.
- 06
Road verification
Charge current, bus voltage, and alternator temperature verified with the engine running under load so we know the system behaves correctly in service.
05
Pricing and posted rates
| Item | Rate or range | Notes |
|---|---|---|
| Typical job range | $750 to $7,500 | Varies with extent of damage and parts availability |
| Shop hours | 4 to 30 | Quoted after teardown, not before |
| Mechanical and electrical labor | $260 per hour | 2026 posted rate |
| Parts | 100% markup under $100, 35% over | Special order parts require a non refundable deposit at order |
| Deposit | 50% at authorization over $2,000 | Additional 25% when parts arrive on jobs over $10,000 |
| Sales tax | 7.75% on parts and materials | Labor is not taxed |
Insurance billed jobs may be billed at carrier negotiated labor rates that differ from the posted retail rates above. See all posted rates.
07
Vehicles we do this work on
Vehicle
Sprinter Vans
Mercedes Sprinter vans run last-mile routes, trade service, and camper conversions across Southern California. Sliding door tracks
Vehicle
Cargo Vans
Cargo vans on Transit, ProMaster, Express, and Sprinter platforms carry trade tools, parts inventory, and route freight. Rear door
Vehicle
Camper Van Conversions
Camper van conversions are Sprinter, Transit, or ProMaster chassis with windows cut into the sidewalls, a roof full of penetration
Vehicle
Class B Camper Vans
A Class B is a camper built inside a factory van shell, usually a Sprinter, Transit, ProMaster, or Chevy chassis. Because the stee
Vehicle
Mobile Medical Clinics
Mobile medical clinics carry exam rooms, imaging or dental equipment, patient access lifts, and climate control that cannot fail w
Vehicle
Mobile Workshops
Mobile workshops carry benches, vises, compressors, welders, and dense tool inventory, which makes weight and mounting the definin
Vehicle
Off-Road and Expedition RVs
Expedition RVs mount a composite habitat box on a four wheel drive truck chassis, usually through a torsion-free three or four poi
08
Questions about auxiliary battery and dc-dc charging systems
Frequently asked questions
Why do I need a DC-DC charger instead of a battery isolator?
An isolator just connects the banks together. A lithium bank will pull everything the alternator can make and hold it there, which overheats an alternator that was never rated for sustained full output. A DC-DC charger limits that current and delivers a correct charge profile. On smart alternator vehicles it also boosts a low bus voltage into a real charge voltage.
What does an auxiliary battery system cost?
Work runs $750 to $7,500, or 4 to 30 hours at $260 per hour plus equipment. A single group 31 AGM auxiliary battery with a 20 amp DC-DC charger in a cargo van is at the low end. A 400 amp hour LiFePO4 bank with a 60 amp charger, long cable runs, monitoring, and solar integration in a Sprinter is at the high end.
Will this hurt my alternator?
Not when it is sized correctly, which is the entire point. We measure the alternator rating and set the DC-DC current limit below what it can sustain at idle with the engine fan and air conditioning running, since that is the worst case. The failures we see are from unlimited isolator connections, not from properly limited DC-DC installs.
Can you add house power to a work van or fleet vehicle?
Yes. Auxiliary power for refrigeration, medical equipment, tools, lighting, and inverter loads is a regular part of our fleet upfit work. We size the bank to a full shift of actual load, protect the starting battery so the vehicle always starts, and label the system so a driver can troubleshoot the basics.
Does this work with solar at the same time?
Yes, and it should. Solar and DC-DC charging feed the same bank and need coordinated charge profiles so they are not fighting each other over absorption voltage and timing. We set both to the same chemistry targets and add a shunt monitor so you can see which source is contributing at any moment.
09
Related services
Service
House Battery Replacement, AGM and Lithium
House battery replacement covers flooded lead acid, AGM, and LiFePO4 lithium bank builds, including the charging profile and cable
Service
Solar Panel Installation and Repair
Solar installation covers roof panel mounting, MPPT controller sizing, wire routing, and integration with an existing battery bank
Service
Inverter and Charger Replacement
Inverter and charger replacement covers failed units, capacity upgrades, and modified sine to pure sine conversions, including tra
Service
Custom Van Build-Out and Camper Conversion
A custom van build-out converts an empty cargo van into a camper, mobile workshop, or purpose-built work vehicle with insulation,
Service
12V and 120V Electrical Diagnostics and Repair
Electrical diagnostics traces 12V DC and 120V AC faults on RVs, vans, trailers, and fleet units, including dead circuits, parasiti
10
More electrical and systems work
Ready to move on auxiliary battery and dc-dc charging systems? Bring it to Yorba Linda.