Correct alternator for 2.4 engine, but might just be battery

[Alpha Hydrae]

My 2002 2.4 Alphard's engine wouldn't turn over yesterday, which was odd as I'd used it a few times this week. There was some clicking, and all electrical items such as lights/radio/central locking are working fine. I managed to jump start it using a big heavy duty charger/booster - this was following about 5 minutes charge on the 'High' setting, and I drove about 5 miles away and parked it. It ran as smooth as ever when driving. A hour later it wouldn't start again. Tried jump starting from a friend's Aygo but either it was too small, or his jump leads weren't up to it, but I could hardly even get my engine to turn over.

 

I've purchased a new battery and planning to head over to where the car is and replace it. However, I've remembered something else. For the past couple of months I've noticed my interior leisure battery had been dying quicker than normal (the 12-240V convertor beeps when its 12V source is too low). I assumed it was just my kids plugging in phone chargers more than usual, and I also thought maybe the split-charge relay was failing, but I'm now wondering it was an early sign that my alternator was failing. And perhaps now the alternator isn't giving enough charge to the main battery. As I said, the engine started and ran fine using the booster.

 

I suspect if I fit the new battery it'll start OK, but in a couple of days I might be back where I started and have wasted money on a battery I didn't need.

 

Hence I'm wondering if I need to also buy an alternator and replace that in-situ (I should point out I don't have a breakdown recovery subscription, which I know is silly, but there's a valid reason which is another story entirely !).

 

Any thoughts on this? Advice for alternator model ? I'd obviously prefer a Denso, but can't keep everything original all the time.

[Rojie]

13 hours ago, Alpha Hydrae said:

My 2002 2.4 Alphard's engine wouldn't turn over yesterday, which was odd as I'd used it a few times this week. There was some clicking, and all electrical items such as lights/radio/central locking are working fine. I managed to jump start it using a big heavy duty charger/booster - this was following about 5 minutes charge on the 'High' setting, and I drove about 5 miles away and parked it. It ran as smooth as ever when driving. A hour later it wouldn't start again. Tried jump starting from a friend's Aygo but either it was too small, or his jump leads weren't up to it, but I could hardly even get my engine to turn over.

 

I've purchased a new battery and planning to head over to where the car is and replace it. However, I've remembered something else. For the past couple of months I've noticed my interior leisure battery had been dying quicker than normal (the 12-240V convertor beeps when its 12V source is too low). I assumed it was just my kids plugging in phone chargers more than usual, and I also thought maybe the split-charge relay was failing, but I'm now wondering it was an early sign that my alternator was failing. And perhaps now the alternator isn't giving enough charge to the main battery. As I said, the engine started and ran fine using the booster.

 

I suspect if I fit the new battery it'll start OK, but in a couple of days I might be back where I started and have wasted money on a battery I didn't need.

 

Hence I'm wondering if I need to also buy an alternator and replace that in-situ (I should point out I don't have a breakdown recovery subscription, which I know is silly, but there's a valid reason which is another story entirely !).

 

Any thoughts on this? Advice for alternator model ? I'd obviously prefer a Denso, but can't keep everything original all the time.

 

Hello Ben,

 

The clicking indicates, to me, that your battery needs charging.

What happens with all the dash lights when trying to start.

 

It is essential on these vehicles to maintain a full charge; vital in winter

 

I would disconnect the inverter, and the leisure battery, and try again after a full charge.

I would remove the leisure battery for charging, just to isolate the two batteries

I doubt your split charger is failing.

 

I have a smart charger, a CTEK, which will charge the battery, indicate the level of charge, and test the alternator.

Check your mood lighting is off in the dark, not during the day.

 

IF you do buy another battery, keep the old one (unless it is totally shot) in your garage on charge; it will give you a back-up.

Measure the old battery, off load, and ensure the voltage is around 12v; anything around 10,5 and it is shot.

The battery should be 12.6 or so.

 

 

[Alpha Hydrae]

On 9/6/2025 at 9:20 AM, Rojie said:

 

Hello Ben,

 

The clicking indicates, to me, that your battery needs charging.

What happens with all the dash lights when trying to start.

 

It is essential on these vehicles to maintain a full charge; vital in winter

 

I would disconnect the inverter, and the leisure battery, and try again after a full charge.

I would remove the leisure battery for charging, just to isolate the two batteries

I doubt your split charger is failing.

 

I have a smart charger, a CTEK, which will charge the battery, indicate the level of charge, and test the alternator.

Check your mood lighting is off in the dark, not during the day.

 

IF you do buy another battery, keep the old one (unless it is totally shot) in your garage on charge; it will give you a back-up.

Measure the old battery, off load, and ensure the voltage is around 12v; anything around 10,5 and it is shot.

The battery should be 12.6 or so.

 

 

Hi, I took out the old battery and it was exactly as you say, shot ! I've seen this before when one of the 6 cells dies and only gives about 10.6V max. I put a new battery in, engine started immediately, problem solved.

 

When I got home I checked everything with my CTEK MX5 and alternator is fine.

 

I meant to say there is an isolation switch between the 2 batteries, and I'd already used this to cut-off the feed to the leisure battery.

 

I realise now why the leisure battery kept going flat, I'd forgotten the split relay is a 'smart' version that isolates if the supply voltage drops below about 12V. So my leisure battery would probably have only been getting some charge when the engine was running, and I'd not been using the car much throughout summer. I don't know exactly what voltage it would have been receiving when the engine was running. It takes its feed directly from the main battery (not the alternator) so the supply voltage might have been getting dragged down to near the split relay cut-off threshold.

 

As for why one of the cells failed on the main battery, I'll never know. It's at the local recycling centre now.

[Rojie]

10 hours ago, Alpha Hydrae said:

Hi, I took out the old battery and it was exactly as you say, shot ! I've seen this before when one of the 6 cells dies and only gives about 10.6V max. I put a new battery in, engine started immediately, problem solved.

 

When I got home I checked everything with my CTEK MX5 and alternator is fine.

 

I meant to say there is an isolation switch between the 2 batteries, and I'd already used this to cut-off the feed to the leisure battery.

 

I realise now why the leisure battery kept going flat, I'd forgotten the split relay is a 'smart' version that isolates if the supply voltage drops below about 12V. So my leisure battery would probably have only been getting some charge when the engine was running, and I'd not been using the car much throughout summer. I don't know exactly what voltage it would have been receiving when the engine was running. It takes its feed directly from the main battery (not the alternator) so the supply voltage might have been getting dragged down to near the split relay cut-off threshold.

 

As for why one of the cells failed on the main battery, I'll never know. It's at the local recycling centre now.

 

Interesting that you have a smart split relay set-up. Why ?

 

If you have certain types of voltage sensitive units they are designed to allow your leisure battery to pass charge to your starter battery.

Good idea ? Sometimes !

 

If your starter battery fails, as yours did, your leisure battery will try to assist it, as you suspect.

The problem is that leisure batteries are not designed to start vehicles, most have low CCA specifications.

 

Furthermore, the cabling from the leisure battery will not be designed to take starting current.

The voltage drop will, most likely, be excessive thereby not providing enough voltage or current to be able to crank the engine.

 

If your leisure battery is at the back of your vehicle, as mine is, the drop will be even more.

 

I have a CTEK MX5, and can recommend them.

You can even get leads to  'permanently fit to your battery which lowers the risk of accidents when connecting / disconnecting.

 

Your alternator should output close to 14v.

 

I use a cheap voltmeter in the cigarette socket to monitor voltages when on the move; effectively checks the alternator output and the battery becoming fully charged.

I move it to the rear leisure battery sockets when parked up.

 

Glad you sorted it.

 

If you do not use the vehicle much in winter, you must keep that starter battery fully charged.

 

 

[Alpha Hydrae]

I might be using the wrong terminology, but mine is a voltage sensitive relay that only allows current inbound from the main battery. I'm quite happy with it that way. You're correct that it means I can't use the leisure battery to provide backup if I get flat main battery. But that's a risk I'm willing to take as it's about 15 years since I last needed a jump start and that was a camping trip in the days before I had a dedicated leisure battery to be used for charging phones etc. This recent incident was an actual battery failure, and again I'm willing to accept the risk as it's very low likelihood it'll fail suddenly while I'm away from home.

[Rojie]

5 hours ago, Alpha Hydrae said:

I might be using the wrong terminology, but mine is a voltage sensitive relay that only allows current inbound from the main battery. I'm quite happy with it that way. You're correct that it means I can't use the leisure battery to provide backup if I get flat main battery. But that's a risk I'm willing to take as it's about 15 years since I last needed a jump start and that was a camping trip in the days before I had a dedicated leisure battery to be used for charging phones etc. This recent incident was an actual battery failure, and again I'm willing to accept the risk as it's very low likelihood it'll fail suddenly while I'm away from home.

 

I carry jump leads, they are not expensive.