# Optima RTU-4.2 · Car battery 12V 50Ah 815A

![Optima RTU-4.2 · Car battery 12V 50Ah 815A](https://bateriasonline.es/3873-home_default/optima-rtu-4-2.jpg)

> Optima RTU-4.2 (ETN 804250000): 50 Ah car battery, 815 A (EN), 254×175×200 mm, positive terminal on the left. Equivalent to Optima RTC-4.2.

**Category:** [Car batteries](https://bateriasonline.es/en/car-batteries) → [Optima](https://bateriasonline.es/en/optima-batteries)

- **Canonical URL**: https://bateriasonline.es/en/optima-rtu-4-2
- **Language**: en
- **Brand**: Optima
- **Reference**: BOL-OPTIMA-RTU-4.2
- **EAN**: 4016987113486
- **MPN**: RTU-4.2
- **Price**: 181,81 € (VAT incl., Spain)
- **Last updated**: 2026-10-27

## Technical specifications

| Feature | Value |
|---|---|
| Brand | Optima |
| Range | OPTIMA RED TOP |
| Application | Cars |
| Technology | Spiral AGM |
| Voltage | 12 V |
| Capacity | 50 Ah |
| Cold cranking amps (EN) | 815 A |
| Length | 254 mm |
| Width | 175 mm |
| Height | 200 mm |
| Weight | 18.4 kg |
| Polarity | Positive terminal on the left |
| Terminal type | 1 & 21 |
| ETN code | 804250000 |

## Quick description

The Optima RTU-4.2 (ETN 804 250 000, also written 804250000) is a car battery (spiral AGM) with 12 V, 50 Ah and 815 A cold cranking current, measuring 254 × 175 × 200 mm, with the positive terminal on the left. With the positive terminal on the right, the exact counterpart is the Optima RTR-4.2.

## Description

## The Optima RTU-4.2 at a glance

The Optima RTU-4.2 is a starter battery for cars without Start-Stop: it delivers the current the starter motor needs and then powers lights, control units and audio with the engine off. The RTU-4.2 covers the daily routine of a car without automatic engine stop: cold starts, short trips and loads with the ignition off.
At 50 Ah it covers petrol compacts and small diesels, the best-selling format in Europe. The RTU-4.2 belongs to the Optima OPTIMA RED TOP range. [See all Optima batteries](https://bateriasonline.es/en/optima-batteries)

## Optima RTU-4.2 vs RTS-3.7, RTR-4.2 and RTU-3.7: which one to choose?

Torn between the RTU-4.2 and another similar Optima? This is what changes:

| Model | Capacity | Cold cranking (EN) | Dimensions (mm) | Positive | Weight |
|---|---|---|---|---|---|
| Optima RTU-4.2 (this one) | 50 Ah | 815 A | 254 × 175 × 200 | left | 18.4 kg |
| Optima RTS-3.7 | 44 Ah | 730 A | 237 × 172 × 197 | left | 15.6 kg |
| Optima RTR-4.2 | 50 Ah | 815 A | 254 × 175 × 200 | right | 18 kg |
| Optima RTU-3.7 | 44 Ah | 730 A | 237 × 172 × 197 | left | 15.7 kg |

- Optima RTS-3.7: 6 Ah less, 85 A less cranking power, a different case (237 × 172 × 197 mm).
- Optima RTR-4.2: identical to the RTU-4.2 except for the positive terminal, which is on the other side (positive terminal on the right).
- Optima RTU-3.7: 6 Ah less, 85 A less cranking power, a different case (237 × 172 × 197 mm).

## Optima RTU-4.2 codes and part numbers

Look for any of these RTU-4.2 codes on your current battery or in the manufacturer's catalogue:

| Commercial reference | RTU-4.2 |
|---|---|
| ETN code | 804250000 (also 804 250 000) |
| EAN | 4016987113486 |
| Same ETN as | Optima RTF-4.2 |
| Case size according to Optima | 34/78 (BCI) |
| Base hold-down | B00 |
| Terminal type | 1 & 21 |
| Also known as | Optima 804250000 · Optima 804 250 000 |
| Not to be confused with | Optima RTC-4.2 (50 Ah, 815 A), Optima RTR-4.2 (50 Ah, 815 A, positive terminal on the right), Optima YTU-4.2 (55 Ah, 765 A) |

## Equivalents and alternatives to the Optima RTU-4.2

As the RTU-4.2 is an AGM battery, we only list other AGM batteries with its dimensions and polarity: neither an EFB nor a conventional battery can replace it.

| Model | Technology | Capacity | Cold cranking (EN) | Dimensions (mm) |
|---|---|---|---|---|
| Optima RTC-4.2 | Spiral AGM | 50 Ah | 815 A | 254 × 175 × 200 |
| Optima RTS-4.2 | Spiral AGM | 50 Ah | 815 A | 254 × 175 × 200 |

## Check this before ordering the Optima RTU-4.2

- The RTU-4.2 needs 254 × 175 × 200 mm of space: measure it with the hold-down clamp in place.
- Polarity of the RTU-4.2: positive terminal on the left (if yours has it on the other side, the cables will not reach).
- Your current battery should say about 50 Ah; a little more is also fine.
- Check the EN amps on your battery: if it says 815 A or less, the RTU-4.2 covers your engine.
- The RTU-4.2 is AGM: it replaces an AGM or an EFB of the same size. You can swap an EFB for an AGM, but not an AGM for an EFB.

## What it means that the RTU-4.2 is spiral AGM

The RTU-4.2 is a spiral-cell AGM battery. Perfect for 4x4s, marine use and vehicles with lots of electronics.

## Frequently asked questions about the Optima RTU-4.2

### Optima RTU-4.2 or RTS-3.7?

Compared with the RTU-4.2, the Optima RTS-3.7 has 6 Ah less and 85 A less cranking power. The RTU-4.2 cranks harder; the RTS-3.7 is only a good option if your original battery says 730 A or less. Mind the space: the RTS-3.7 measures 237 × 172 × 197 mm.

### What is the difference between the Optima RTU-4.2 and the RTR-4.2?

They are the same battery with the terminals swapped: positive terminal on the left on the RTU-4.2, positive terminal on the right on the RTR-4.2. Look at your current battery with the terminals facing you and pick the one that matches. That is why their ETNs only differ in the middle group: 804 250 000 for the RTU-4.2 and 803 251 000 for the RTR-4.2.

### What is the ETN code of the Optima RTU-4.2?

804250000, also written 804 250 000. The ETN (European Type Number) is printed on the label and used in parts catalogues.

### Can the Optima RTU-4.2 be used in a car with Start-Stop?

Yes. As an AGM battery, the RTU-4.2 handles automatic engine stop and brake energy recovery, and it can replace an EFB of the same size.

### How much does the Optima RTU-4.2 weigh?

The RTU-4.2 weighs 18.4 kg. For reference, the Optima RTS-3.7 (44 Ah) weighs 15.6 kg.

### Which battery is equivalent to the Optima RTU-4.2?

Only other AGM batteries with its dimensions and polarity: Optima RTC-4.2 and Optima RTS-4.2. Neither an EFB nor a conventional battery replaces the RTU-4.2.

## More batteries to compare with the RTU-4.2

- [Other car batteries](https://bateriasonline.es/en/car-batteries)
- [More Optima models](https://bateriasonline.es/en/optima-batteries)
- [Optima RTC-4.2](https://bateriasonline.es/en/optima-rtc-4-2) · 50 Ah, 815 A, 254×175×200 mm
- [Optima RTS-4.2](https://bateriasonline.es/en/optima-rts-4-2) · 50 Ah, 815 A, 254×175×200 mm

---
*bateriasonline.es — Batteries and accessories · 2026-11-10*