Why people are switching to lithium batteries
Lithium batteries are popular because they are:
- Lighter
- More efficient
- Take up less space
But not all vehicles or systems are built for them, so switching needs to be done properly.
Types of batteries
1. Lead-acid (standard/wet batteries)
- Filled with liquid acid.
- When used, the acid turns into water and releases energy.
- When charged, it turns back into acid.
- Cheapest option, but heavier and doesn’t last as long.
2. AGM (Absorbent Glass Mat)
- Still a lead-acid battery, but the liquid is soaked into a special mat.
- Pros:
- Safer (no spilling)
- Handles vibrations better
- Charges faster than standard lead-acid
- Cons:
- More expensive than standard lead-acid
- Still heavy
3. Gel batteries
- Another type of lead-acid battery, but the acid is turned into a gel.
- Pros:
- Very safe and spill-proof
- Good for slow, steady power use
- Cons:
- Sensitive to overcharging
- Slower to charge
- Not great for high power demands
4. Lithium batteries
- Use completely different materials (no liquid acid).
- Pros:
- Much lighter
- Last longer
- Can be used more deeply without damage
- Cons:
- More expensive upfront
- Need the correct charger and system setup
Why lithium behaves differently
Because lithium uses different materials, it:
- Charges and discharges differently
- Lasts longer with repeated use
- Needs a different type of charger than lead-acid, AGM, or gel
Why lithium behaves differently
Because lithium uses different materials, it:
- Charges and discharges differently
- Lasts longer with repeated use
- Needs a different type of charger than lead-acid, AGM, or gel
What is “terminal voltage”?
- This is the voltage where the battery is considered fully charged
- For most lead-acid, AGM, and gel batteries: about 14.4 volts
How charging works (simple)
- The charger has a higher voltage than the battery
- Power flows from the charger into the battery
- This recharges it
Key takeaway
- AGM and gel are improved versions of lead-acid
- Lithium is a bigger upgrade but needs the right setup
- Using the wrong charger (especially with lithium) can cause problems
A lead-acid battery that has not been charged for several weeks may sit at around 12.4V. When a battery charger is connected and switched on, it produces a terminal voltage of 14.4V. This creates a 2V difference, known as a voltage potential gradient.
It is this gradient that allows current to flow from the charger into the battery.
This passage is explaining why a standard (lead-acid) charger is not suitable for fully charging a lithium battery, even though it might appear to work.
Here’s a clearer breakdown:
Invite team members
yet reached its fully charged voltage of 14.6V. It is this issue that necessitates upgrading the charger and other systems in your vehicle when fitting lithium batteries. With a lithium battery, the terminal voltage is 14.6V as determined by the internal chemical make-up of the battery. 0.2V difference may not seem like a lot, but not reaching the battery’s terminal voltage can mean as much as 25-30% of the battery capacity is not recharged! Given the higher cost of lithium batteries over lead acid, if you are purchasing one it would make sense to use all of it! As you can see in Figures 3 and 4, the traditional charger will still charge a lithium battery, however as Figure 5 shows to fully charge a lithium battery it needs to be connected to a lithium charger with a higher terminal voltage.
So why is a standard (lead-acid, agm, gel) charger not suitable for fully charging a lithium battery, even though it might appear to work.
Here’s a clearer breakdown:
- Lithium batteries require a higher charging voltage (around 14.6V) due to their chemistry.
- Traditional chargers (designed for lead-acid batteries etc) typically charge to a slightly lower voltage (around 14.2–14.4V).
- That small difference (~0.2V) might seem minor, but it has a big impact on capacity:
- The battery may only reach 70–75% charge
- Meaning 25–30% of usable capacity is lost
- So while a normal charger can charge a lithium battery, it cannot fully charge it.
- Because lithium batteries are more expensive, not charging them fully means:
- You’re not getting the full value or performance
- You may need to upgrade:
- The charger
- Possibly other vehicle charging systems (e.g., alternator, DC-DC charger)
1. Upgrade your mains charger first
Lithium batteries need a higher charging voltage (around 14.6V) than lead-acid (around 14.4V).
👉 So your existing charger may never fully charge a lithium battery.
➡️ Solution: install a lithium-compatible charger.
2. What happens when you drive (engine charging)?
When your engine runs, the alternator charges your batteries.
There are two common setups:
✅ Modern system (with a booster / DC-DC charger)
- Uses a Battery-to-Battery (B2B) charger / DC-DC charger
- Keeps starter battery and leisure battery separate
- Converts alternator output into a stable, correct voltage
- Often has a lithium mode (14.6V output)
👉 This is ideal for lithium. Just switch to lithium mode.
⚠️ Older system (split charge relay)
- Simply connects both batteries together
- Assumes both batteries have similar voltage (works for lead-acid)
👉 Problem with lithium:
- Lithium battery sits at higher voltage
- This creates a voltage mismatch
⚠️ Older system (split charge relay)
- Simply connects both batteries together
- Assumes both batteries have similar voltage (works for lead-acid)
👉 Problem with lithium:
- Lithium battery sits at higher voltage
- This creates a voltage mismatch
3. ❗ Why this causes problems
Because lithium (≈14.6V) and lead-acid (≈14.4V) have different voltages:
- Power can flow the wrong way
- Your leisure (lithium) battery can discharge into the starter battery
- You may actually lose charge while driving
👉 Yes—driving could drain your leisure battery instead of charging it.
4. ⚠️ The “loop” problem
If you add a booster but leave the old split-charge system in place:
- The booster tries to control charging properly
- The old system still links batteries directly
👉 This creates a charging loop / conflict, reducing efficiency or causing issues.
✅ Best practice when converting to lithium
- Install a lithium-compatible mains charger
- Replace or disable split charge relay
- Install a DC-DC (B2B) charger with lithium mode
- Ensure system is properly isolated (no direct battery linking)
🧠 Bottom line
- Old systems = simple but incompatible with lithium
- Lithium needs controlled charging, not direct connection
- A DC-DC charger (booster) is the key upgrade for safe and effective charging while driving
