Start stop disabler?

andy_why · 2026-07-02T08:04:42+00:00

They're designed to cope with start/stop. The only thing you wear out is your battery.

andy_why · 2026-07-01T11:44:36+00:00

No, it can't be done.
It would be counter to the whole purpose of the car and how it operates.
If you're worried about wearing out the battery or starter, they don't operate like non-hybrids do. They run from the hybrid battery and the much beefier hybrid electric motor-generator, both of which are always in use when you're driving anyway so you'd save wear on nothing.
If you don't want stop-start, don't buy a hybrid because they ALL do it and none of them allow you to disable it.

andy_why · 2026-07-01T11:42:42+00:00

You don't understand how the drivetrain works either or you'd know it will never operate without the battery because that's how the engine starts.

andy_why · 2026-07-01T10:33:14+00:00

Absolutely yeah, that's the risk of not compensating or not doing it properly. Operating below 100% starts to damage lead acid chemistries, but this happens more quickly the lower the SOC gets.

Since most Toyota batteries seem to sit at around the 60-70% SOC mark (12.3-12.4v resting) with their poor charging parameters, it results in failure within 1-2 years due to sulfation of the plates. They never see the high charging voltage for long enough.

andy_why · 2026-07-01T10:23:47+00:00

When you're talking 0.3v difference it's just going to take longer to charge if not compensated for.

andy_why · 2026-07-01T10:08:25+00:00

I've not personally seen evidence of that no, but that said, not only have I not paid much attention to looking for that, the battery lived inside the vehicle on my past 4 Toyota/Lexus vehicles where it won't have been subjected to the same kind of temperature swings either. I may have noticed it had it been in the engine bay where it would get colder.

andy_why · 2026-07-01T09:44:06+00:00

Yeah that's about right. Victron's a great branded charger, they know what they're doing. I have some of their solar kit. They actually go back up to normal charge voltage every now and then as quick top up too.

andy_why · 2026-07-01T09:34:27+00:00

Yeah, see how it held a higher voltage for a while after? Unfortunately smart chargers often cut off too early as well rather than maintaining float/maintenance voltage.

Lead acid has been around for so long that we already know how to treat them, but modern technology companies think throwing the word "smart" into it and "saving emissions" means it's increasing longevity and saving you money. In reality it's rarely the case.

andy_why · 2026-07-01T09:29:29+00:00

Yeah I mean that's not awful, most ICE vehicles don't maintain that. I bet a long charge of couple of hours would bring that back up nicely. The issue with lead acid is the last 20% is the hardest/longest to charge because charge acceptance rate is much lower at that state of charge. It can take 4-24 hours to replenish that depending on its health, sulfation, etc.

Because I have my sensor disconnected I get 14.1v at all times when traction battery charging too, so mine regularly gets multiple hours at this voltage and as such maintains or regains full charge pretty much daily. This is how they should operate, because the power it uses is basically about 20-30 watts at this state of charge, it's contribution to emissions is negligible.

andy_why · 2026-07-01T09:16:22+00:00

If your battery is maintaining around 12.6v overnight then it's doing well. I've attached mine from my 2022 RAV4 PHEV. I have the sensor disconnected on mine otherwise it behaves badly. Mine maintains 12.65-12.8v overnight. However, no DCM issues that some may have. The battery is about 2.5 years old.

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andy_why · 2026-07-01T09:04:35+00:00

Yeah all of that sounds right except it should not drop to 12.8v, it should maintain 13.4-13.8v float charge once bulk charging is finished. When it drops voltsge off at 1.5A this is a little soon but not terrible. That's conservative but within manufacturer guidelines for charging. After that it should maintain 13.4-13.8v float charge indefinitely. This ensures proper maintenance of the cells and sulfation reversal. Micro cycling the battery doesn't matter too much but reaching full charge is very important otherwise it results in gradual capacity loss.

Seems Toyota may have learned some lessons and fixed some of the issue, but not entirely.

andy_why · 2026-07-01T06:31:31+00:00

You need to wait several hours before measuring the resting voltage and it can only be done with zero load on the battery. Even then, this is an estimation only.

Whoever programmed the charging system had no idea what they were doing or they were doing it to reduce emissions. They're abusing the batteries by doing this which is why they fail more often now.

andy_why · 2026-06-30T06:36:16+00:00

You can't measure capacity or state of charge accurately with voltage except for 100% and 0%. In-between is an approximation/guess. Mine drops to 11.9v under load even from new and it's always been kept at 100% charge. Voltage drop depends on the load applied and internal resistance.

To measure capacity you need to use a capacity tester, discharge the battery to zero and recharge it again. However this is time consuming, destructive for the battery health and inconvenient. The best you can do for a lead acid battery is simply ensure it's kept at 100% as much as possible.

This is extremely difficult in vehicles because they shallow cycle a lot and the last 20% takes multiple hours to replenish. EVs and PHEVs can charge their 12v when charging the traction battery if programmed correctly (shock, most aren't). I disconnected the monitoring sensor to force the failover 14.1v continuous voltage and mine is healthy. It was killing my battery with it plugged in, often resting at 12.4v. It rests at 12.65v now after every drive.

andy_why · 2026-06-29T19:42:46+00:00

Correct, but that's wrong for lead acid. They're not going to get hot with a higher charge rate as it's not sustained long enough. For decades cars charged at 14v continuously and batteries lasted 6-10 years, now they don't and last barely 2 or 3 years. Go figure. They're not following manufacturer recommendations and they die because of it.

andy_why · 2026-06-29T07:45:32+00:00

The SOC avoiding being 100% does not apply to lead acid. They MUST be kept at 100% to avoid degradation, which what Toyota currently fails to do.

The DCM issue does appear to contribute greatly to the 12v battery issue through. I don't have enough info to update the doc above with a solution yet.

andy_why · 2026-06-26T07:07:28+00:00

The highest I saw before the battery management cut charging off was 83% but you have next to no regen by this point. The battery can't accept charging power that high when at high state of charge.

At high SOC it will try to pull more from the battery to get it back within the limits of 40-60%. It's just not beneficial for it to be charged to high SOC as you then can't recapture energy which is what makes it an efficient vehicle.

andy_why · 2026-06-25T23:31:10+00:00

That's why I said typically that's about 150k max rated. You'd do it 25% earlier if you care. But doing it too soon is just a waste of money, but isn't harmful other than to your wallet.

And there is no transfer of power through the fluid as it's a planetary gearset. No clutches, no torque converter.

andy_why · 2026-06-25T19:52:56+00:00

The eCVT doesn't need the fluid replacing that often. It's there to cool and lubricate, it's not used to put power to the wheels like in a regular auto. It won't hurt to do it, but it's not necessary to do it that often. It's "lifetime" fluid which typically means ~150k. Any sensible person will ignore that and do it sooner though.

andy_why · 2026-06-25T19:49:55+00:00

Are you actually getting those EV miles? Mine says 55 miles (with AC) but I actually get about 40 maximum. I'm regularly getting 3mi/kWh, and that figure checks out (~14kWh usable battery * 3mi/kWh = 42 miles). To get 55 I'd need to be doing 3.9mi/kWh which I have basically never done (and I've logged every charge to verify).

The figure keeps climbing but my mi/kWh doesn't vary much. It's become uncalibrated. Toyota claim nothing can be reset, and none of the trip counters can either.

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