This should be the last portable battery charger you ever buy and it's Waterproof!  Temperature sensor included with purchase of the charger.

• Safely charges 70% - 200% faster than any/all known conventional constant voltage chargers. Guaranteed 100% full charge to ALL TYPE / SIZE / BRAND 12-Volt batteries, without ever overcharging them.
• Maximizes cycle life and performance of all three (3) types* of lead-acid storage batteries, regardless of size / type / brand.
• Push button selectable type and charge rates for all size / type / brands of 12- Volt batteries, including flooded (filler caps), sealed Absorb Glass Mat (AGM), and Gel.
• 3 Stage (constant current bulk- constant voltage absorption-pulse width modulated float) ensures 100% full charge capacity of all battery types.
• Full Time random sweep desulphation**.Desulphates faster and more effectively than any known charger or stand-alone desulphator-conditioner.
• Spark-proof, short circuit, reverse polarity and over-temperature protected.
• Automatically detects defective batteries and rejects them.
• Includes built-in soft start for voltages down to 3 volts.  If battery voltage does not increase to 10.5 volts within a predetermined time, the battery is rejected. 
• Polarity reversal-Error indicator.
• Auto-reset thermal breaker (protects both battery and charger under abnormal conditions such as a shorted cell and /or excessively high ambient temperatures)
• Manual override for maintenance- desulphation only long term storage mode.
• Rejects a damaged or open cell (shorted) battery.
• Watertight enclosure with conformal-coated protected circuitry.
• Extremely light weight (2 lbs.) – compact size- 5.5” x 5.5” x 2.25”.
• Portable or OnBoard mountable.
• Built-in battery condition indicators: detect and display charge level modes, charge retention and existence of sulphation.
• Automatic temperature compensation w/ optional battery temperature sensor. Sensor can be used to detect and adjust charger’s output voltage depending on temperature, extending battery life and performance by more than 100%***.
• 1 year 100% Money back Guarantee plus 5 year “no hassle” warranty.
• VDC, the manufacturer, also guarantee model 12248 will significantly increase your battery’s life well beyond any known battery charger currently on the market.  If for any reason you do not find this to be true we will, up to one year after date of purchase, refund 100% of your money, including any taxes or shipping costs ****.

• * Flooded (filler caps), maintenance-free sealed AGM and Gel.
  ** U.S. Patented
  *** When compared to non “at the battery” temperature compensated chargers or ambient sensing types.
  **** Requires registration of product within 10 days of date of purchase and is non-transferable.