Chevrolet, Express, GMC and Savana are trademarks of their owner. Amp Hour Supply isn’t affiliated with General Motors.
Short answer: GM’s charging system on these vans doesn’t hold one fixed voltage. It moves the voltage based on the battery’s charge and temperature, and it counts amp-hours through a sensor on the battery’s negative cable. A lithium house bank belongs behind a DC-DC charger that gets a separate engine-running signal, so charging doesn’t hinge on a voltage GM keeps changing.
The Express and Savana numbers
| What | GM’s figure | Source |
|---|---|---|
| Alternator (“generator”) options | 105 A (K68), 150 A (KG4), 220 A (KW5) | 2025 electrical body builder manual |
| Dual battery option (TP3) | Two batteries, 770 CCA each | 2025 manual |
| How TP3 joins the second battery | Auxiliary Battery Relay KR81, coil on fuse F13 (10 A) | 2024 manual |
| TP3 aux battery ground | G305, left center outer frame rail, near the aux battery | 2025 manual |
| Battery current sensor | On the negative battery cable at the battery | 2024 manual |
| Charging control | Regulated voltage control: voltage set from charge level and temperature | 2024 manual |
| Idle boost (gas) | Starts at a net battery loss over 0.6 AH; more at 1.6 and 10.0 AH | 2025 manual |
| Load shed (gas) | Rear defrost, heated mirrors, heated seats cycled off 20%, then 50%, then 100% of the time at 4, 12 and 20 AH lost (the 12 and 20 AH steps also need low voltage) | 2025 manual |
| Fault fallback | Alternator defaults to 13.8 V if its field control fails | 2024 manual |
How do I charge a lithium battery from a Chevy Express alternator?
Use a DC-DC charger. On this van there are two GM-specific reasons beyond the usual lithium ones.
The voltage moves on purpose. GM’s regulated voltage control picks a charging voltage it thinks is best for the starting battery. That’s good for the starting battery and unpredictable for anything that switches on voltage alone. The Victron Orion-Tr Smart 12/12-30 isolated DC-DC runs on anything from 8 to 17 V in, charges the lithium bank on its own profile, and Victron recommends an engine-running signal on its remote input for alternators like this.
The van is counting. GM’s body control module tracks amp-hours. Lose more than 0.6 AH net and it starts raising idle. Keep losing and it begins cycling off the rear defrost, heated mirrors and heated seats. If the alternator can’t cover a 30 A charger plus the van’s own loads at idle, the starting battery runs a net loss and those steps can kick in. That’s more likely on the 105 A alternator than the 220 A one. If the idle comes up, the van is doing what GM designed it to do.
GM’s manual doesn’t say where an added charger’s negative should land relative to the current sensor, and we won’t guess. Check the ground list in the body builder manual for your year, or ask a GM upfitter.
The general combiner vs DC-DC comparison lives in Charging lithium from a boat alternator: 3 ways compared. Boat-focused, same charger.
You’ll need
- Your van’s RPO codes (glovebox label). Look for K68, KG4 or KW5, plus TP3 and 9L7.
- A Victron Orion-Tr Smart 12/12-30 isolated DC-DC
- A 60 A fuse for the charger input (Victron’s figure)
- An ignition-switched feed for the engine-running signal
- A Victron SmartShunt 500A
- A Victron SmartSolar MPPT 100/30 for roof solar
- GM’s Express/Savana electrical body builder manual for your year
Steps
- Read your RPO codes. The alternator code tells you how much headroom you have. A 220 A van has far more room for a 30 A charger than a 105 A van.
- If you have TP3, note that GM already joins a second battery through relay KR81 and grounds it at G305. Don’t stack your lithium bank onto that relay circuit. Keep the house bank on its own charger.
- Pick a feed point from GM’s manual, rated for the charger’s 60 A input fuse. The 9L7 upfitter fuse block’s ratings are only in the manual’s drawings, so read them there before you use it.
- Mount the charger near the house bank and fuse its input at the source.
- Wire the output to the lithium bank, fused at the battery.
- Connect the engine-running signal to the charger’s remote input.
- Set the lithium profile, add the shunt, then idle the van for a few minutes and watch both the shunt and the idle speed.
Shore power, an inverter feeding outlets, anything 120 V: bring in a licensed electrician.
Does this page fit your van?
It fits a 2024 or 2025 Chevrolet Express or GMC Savana, the years of the two GM manuals we used, gas engine (the idle boost and load shed figures are from GM’s gasoline section).
It doesn’t fit cutaway or chassis-cab builds with an upfitter’s own electrical system, or older vans we didn’t check. For those, use the body builder manual for your model year.
Products for this setup
| Product | Why it’s here |
|---|---|
| Victron Orion-Tr Smart 12/12-30 isolated DC-DC | Takes 8-17 V in, so GM’s moving voltage is fine; 30 A cap. |
| Victron SmartShunt 500A | Your own amp-hour count for the house side. |
| Victron SmartSolar MPPT 100/30 | Roof solar for the house bank, parked or driving. |
| Victron Smart BatteryProtect 100A | Cuts house loads before the bank runs low. |
Prices show live from the store.
Bundles for this job: Dual-battery DC-DC charging kit, Van solar starter kit
Quick answers
What alternator sizes does the Chevy Express come with? GM’s 2025 manual lists 105 A, 150 A and 220 A options (RPO K68, KG4, KW5).
Can I tie a lithium battery into the TP3 dual battery relay? GM’s manual describes TP3 with two 770 CCA batteries and says a replacement battery should match the original’s CCA and amp-hour ratings. Keep lithium on its own DC-DC charger instead.
Why does my Express idle up after I add a house battery? GM’s idle boost starts when the van counts a net battery loss over 0.6 AH. If a charger at idle draws more than the alternator covers, that loss can trigger it.
Sources
- GM Upfitter, 2025 Express/Savana Electrical Body Builder Manual (Feb 2025): https://www.gmupfitter.com/wp-content/uploads/2025/02/MY25-Express-Savana-Electrical-BBM.pdf
- GM Upfitter, 2024 Express/Savana Electrical Body Builder Manual (Oct 2023): https://www.gmupfitter.com/wp-content/uploads/2023/10/24-Express_Savana_Body_Builder_Manual_18553161_2023Oct26.pdf
- Victron Orion-Tr Smart DC-DC Charger Isolated manual (Rev 14, 02/2026): https://www.victronenergy.com/upload/documents/Orion-Tr_Smart_DC-DC_Charger_-_Isolated/34439-Orion-Tr_Smart_DC-DC_Charger-pdf-en.pdf
- Victron SmartSolar MPPT 100/30 & 100/50 datasheet: https://www.victronenergy.com/upload/documents/Datasheet-SmartSolar-charge-controller-MPPT-100-30-&-100-50-EN.pdf
